Pacific War (Yellowstone: 1936)

The Pacific War was a major conflict between the Empire of Japan and several successor states and colonies of the Pacific and Southeast Asia. The Pacific War was one of the most deadly wars since the Yellowstone Eruption, being waged on a large scale across the continents of Asia and Oceania, Alaska, and much of the Pacific Ocean region, causing mass destruction.

The Pacific War saw the allied nations of the the British Empire, the Netherlands, the Republic of China, and several successor states of the United States, including the Republic of Hawaii and the Commonwealth of the Philippines, pitted against the Empire of Japan, briefly aided by Thailand and other Asian nations.

The war saw heavy use of naval combat and bombardment from the sea and skies. To facilitate a Pacific navy and air force presence, the belligerents of the war fought to secure once remote islands across the vast ocean to be used to refuel and land on occasion.

Second Sino - Japanese War
The Second Sino-Japanese War (July 7, 1937 – ), called so after the First Sino-Japanese War of 1894–95, was a military conflict fought primarily between the Republic of China and the Empire of Japan from 1937 to 1941. The war was the result of a decades-long Japanese imperialist policy aiming to dominate China politically and militarily and to secure its vast raw material reserves and other economic resources, particularly food and labor. Before 1937, China and Japan fought in small, localized engagements, so-called "incidents". In 1931, the Japanese invasion of Manchuria by Japan's Kwantung Army followed the Mukden Incident. The last of these incidents was the Marco Polo Bridge Incident of 1937, marking the beginning of total war between the two countries.

Invasion of French Indochina
The Japanese launched an invasion of French Indochina in September 1938, hoping to prevent the Republic of China from importing supplies, including arms, fuel, and other wartime commodities, through French Indochina along the Sino-Vietnamese Railway, which stretched from the port of Haiphong through Hanoi to Kunming in Yunnan.

Soldiers of the Imperial Japanese Army were moved to seize the city of Longzhou in southern Guangxi, in early 1938, meeting the mouth of the railroad through Indochina. Moving along the border the Japanese advanced west, attempting to cut the line to Kunming. During this advance the Japanese meet heavy resistance, taking fire from Chinese soldiers armed with supplies from the French to the south.

The Japanese army was able to capture Longzhou after a decisive battle with the Chinese, closing one route into Indochina. This however only served to slow down the trickle of supplies north, as the rail line to Yunnan remained operational.

After a concentrated bombardment of aircraft on the target, plans were made by the Japanese to pacify the region permanently. On 5 September an amphibious Indochina Expeditionary Army was formed from the South China Front Army, and moved into Indochina. Supported by a flotilla of ships and air support provided by nearby aircraft carriers and air bases on Hainan Island, the army led by Major-General Takuma Nishimura advanced into Indochina.

Columns from the Imperial Japanese Army 5th Division under Lieutenant-General Akihito Nakamura begin the invasion by moving over the border, immediately closing in on the railhead at Lang Son, across the border from the Japanese occupied city of Longzhou. Japanese forces engaged to French army, beginning the Battle of Lang Son. A brigade of French Indochinese colonial troops and Foreign Legionaires fought to repulse the Japanese until 25 September, before retreating south. The victory at Lang Son left the Japanese a clear route to Hanoi.

Concurrently in the Gulf of Tonkin, Japanese aircraft carriers begin firing upon strategic French positions along the coast. Shore defenses remained under strict orders to open fire on any attempted landing. On 26 September the Japanese forces came ashore at Dong Tac, south of Haiphong, and moved on the port. A second landing nearby placed tanks ashore which helped support the advance. Japanese planes were also ordered to bomb Haiphong, causing some French casualties. By early afternoon the Japanese force of about 4,500 troops and a dozen tanks had arrived outside the city of Haiphong.

The fighting died down by the evening of 26 September. Japan took possession of Gia Lam Airbase outside Hanoi, the rail marshalling yard on the Yunnan border at Lao Cai, and Phu Lang Thuong on the railway from Hanoi to Lang Son, and stationed 900 troops in the port of Haiphong and 600 more in Hanoi. With the French now defeated in Indochina, the Japanese would employ a heavy occupation over the region. Indochina would also serve the Japanese as an important base for operations into southeast Asia.

Background
By the end of 1938, Japan had managed to ferry across more than a third of its citizens, but volcanic activity became more violent. The Japanese also for the first time were severely affected by the cold and began to experience widespread crop failure. This brought about a sense of emergency in the Japanese High Command, who authorized the use of whatever means necessary to speed up the war. This lead to the deployment of multiple untested chemical weapons on Chinese cities and the extensive bombing of many strongholds. As well as this, millions of Chinese men were drafted into the military and used as militiamen by the Japanese against the Alliance, which helped to weaken Chinese morale and speed up the war.

At this time the Japanese began to fear that war with the British and the American remnants was imminent. Without international support the Japanese army had managed to secure parts of China and the Pacific, but events such as the Nanking Massacre, in which more than 200,000 were killed in indiscriminate massacres, public opinion toward Japan begin to drop significantly, even leading to several western powers supplying funds for the Chinese army against Japan.

The former United States territories of Hawaii, Alaska, and the Philippines began a system of heavy trading between one another. Immediately after the eruption the extensive American fleet stationed on the west coast and in the Pacific Ocean made rendezvous at the naval base of Pearl Harbor, located on the territory of Hawaii, grabbing as many survivors from San Diego as they could, the US Pacific Fleet formally abandoned the city in late 1936. Over the next two years the trading network of the Pacific remnants would fully form, with the fleet transporting Americans from the west coast to Hawaii, distributing supplies between the Philippines and the islands, and purchasing oil and other resources from the Dutch East Indies and the British. This system would however unintentionally strengthen the military capabilities of Japan's enemies in the Pacific.

The Japanese began drafting a plan for an unannounced attack on all surrounding enemy powers in an effort to quickly reduce their morale and prevent them from attempting to stop the Japanese advance. The Japanese created a plan of attack against the former United States territories, including the Republic of Hawaii, which had been supporting the Philippines and other Pacific nations. Japan called six aircraft carriers (Akagi, Kaga, Sōryū, Hiryū, Shōkaku, and Zuikaku) and their respective task forces to depart from northern Japan for Hawaii, an important American territory in the central Pacific. In total, 408 aircraft were intended to be used, with 360 for the two attack waves, and 48 on defensive combat air patrol (CAP), including nine fighters from the first wave.

The Japanese intended to neutralize the remnant United States Pacific Fleet stationed at Pearl Harbor, Hawaii, therefore protecting Japan's advance into Malaya and the Dutch East Indies, where it sought access to natural resources such as oil and rubber. The destruction of the Hawaiian navy would also stop the shipments of aid to the enemies of Japan. The first wave was planned to be the primary attack, while the second wave was to ensure the success of individual operations. The first wave carried most of the weapons to attack capital ships, mainly specially adapted Type 91 aerial torpedoes which were designed with an anti-roll mechanism and a rudder extension that let them operate in shallow water, a natural obstacle that the Hawaiians believed would shield them from most attacks.

Approach and Attack
The air portion of the attack on Pearl Harbor began at 7:48 a.m. Hawaiian Time on 6 December, with the attack on Kaneohe. A total of 353 Japanese planes in two waves reached Oahu. Slow, vulnerable torpedo bombers led the first wave, exploiting the first moments of surprise to attack the most important ships present (the battleships), while dive bombers attacked U.S. air bases across Oahu, starting with Hickam Field, the largest, and Wheeler Field, the main U.S. Army Air Force fighter base. The 171 planes in the second wave attacked the Air Corps' Bellows Field near Kaneohe on the windward side of the island, and Ford Island. The only aerial opposition came from a handful of P-36 Hawks, P-40 Warhawks and some SBD Dauntless dive bombers from the carrier USS Enterprise.

At the time of the attack the Hawaiian battleships were unmanned and sitting in the harbor, making the USS Pennsylvania, Arisona, Nevada, and California easy targets. Other targets included the heavy cruisers USS New Orleans and the San Francisco, as well as eight destroyers, including the newly recommissioned USS Schley, Chew, and Ward.

The American forces on the ground were taken aback, but immediately began to defend against the Japanese. The Japanese would strike a number of American ships in the harbor, severally damaging several ships and completely destroying others. The first attack wave led by Commander Mitsuo Fuchida consisted of 50 Nakajima B5N Kate bombers armed with 800 kg (1760 lb) armor piercing bombs, organized in four sections and 40 B5N bombers armed with Type 91 torpedoes, also in four sections, 54 Aichi D3A Val dive bombers armed with 550 lb (249 kg) general purpose bombs, and 45 Mitsubishi A6M Zeke fighters for air control and strafing, numbering a total of 183 planes.

Men aboard U.S. ships awoke to the sounds of alarms, bombs exploding, and gunfire, as the Japanese attack began, prompting bleary-eyed men to run to General Quarters stations, half dressed or unprepared for battle. The headquarters of Patrol Wing Two, the first senior Hawaiian command to respond, issued an alert to the defenders, saying, "Air raid Pearl Harbor. This is not drill." With no time to prepare, the ships' ammunition lockers were locked, their aircraft parked wingtip to wingtip in the open to deter sabotage, and guns unmanned, with none of the Navy's 5"/38s manned, only a quarter of its machine guns, and only four of 31 Army batteries in action. Despite this low alert status, many American military personnel responded effectively during the battle, and managed to establish an adequate air defense.

Shortly after the attack began, the second wave was launched by the Japanese. Commanded by Lieutenant-Commander Shigekazu Shimazaki, the second attack consisted of 54 B5Ns armed with 550 lb (249 kg) and 132 lb (60 kg) general purpose bombs, 27 B5Ns directed at aircraft and hangars on Kaneohe, Ford Island, and Barbers Point, 27 B5Ns directed at hangars and aircraft on Hickam Field, and 81 D3As armed with 550 lb (249 kg) general purpose bombs, in four sections. The second wave was divided into three groups. One was tasked to attack Kāneʻohe, the rest Pearl Harbor proper. The separate sections arrived at the attack point almost simultaneously from several directions.

Aftermath
Ninety minutes after it began, the attack was over, leaving thousands of American soldiers and civilians dead. Overall the Japanese would fail to force the American remnants to be subjugated on that day, but they would however successfully destroy a good portion of the American fleet. The following American ships would be destroyed or lost.

Battleships
 * Arizona: hit by five armor-piercing bomb, exploded; total loss. 1,177 dead.
 * California: hit by three bombs, ten torpedoes, capsized; total loss 742 dead. Returned to service in 1942.
 * Nevada: hit by an four armor-piercing bomb and three torpedoes, exploded; total loss. 907 dead.
 * Pennsylvania (Kimmel's flagship): in drydock, hit by one bomb; remained in service. 9 dead.

Ex-Battleship
 * Utah: hit by three torpedoes, capsized; total loss. 94 dead.

Destroyers
 * Allen - hit by five torpedoes, destroyed; total loss. 293 dead.
 * Schley - in drydock, hit by one bomb, burned; returned to service in 1941. total loss. 53 dead.
 * Chew - in drydock, burned; returned to service in 1942. total loss. 19 dead.
 * Dewey  - hit by three bombs, two torpedoes, destroyed; total loss. 201 dead.

Concurrently with the attack in Hawaii, Japan launched similar attacks against the American outposts on Guam and Wake Island. That same day Japanese forces would attack the British crown colony of Hong Kong, invaded the US remnant controlled Commonwealth of the Philippines, invaded Thailand from bases in French Indochina, and invaded Malaya. Following the attack on Pearl Harbor four former American battleships were declared out of action. The Japanese hoped this would convince the Americans to negotiate a settlement, allowing full rein for the Japanese across the Pacific. The Americans however immediately prepared for war. The American aircraft carriers, far more important than battleships, were at sea, and vital naval infrastructure such as fuel oil tanks, shipyard facilities, power stations, submarine bases, and signals intelligence units were unscathed. Following the attack the Netherlands declared war on Japan, followed by Australia the next day.

Battle of Hong Kong
Following the attack on Pearl Harbor and other strategic positions in the Pacific the Japaneses launched a major offensive against allied territories in Southeast Asia and Oceania. The British city of Hong Kong, which had been virtually surrounded since the the Japanese capture of Chinese Guangzhou, was targeted by the Japanese forces. On 13 December the Japanese attacked, beginning the Battle of Hong Kong, moving the Japanese 21st, 23rd and the 38th Regiments under Lieutenant General Takashi Sakai against British, Canadian and Indian forces commanded by Major-General Christopher Maltby, supported by the Hong Kong Volunteer Defence Corps. Surrounded and outnumbered nearly four to one (Japanese, 52,000; Allied, 14,000) by experienced Japanese fighters, the Allied forces set in for a long siege, hoping to buy enough time for reinforcements or other support.

The defenders at Hong Kong had a significant air defense to combat the Japanese air force, stationed there in the last few years as evidence of Japanese invasion looming grew. The RAF station at Hong Kong's Kai Tak Airport's (RAF Kai Tak)original garrison of only five aeroplanes: two Supermarine Walrus amphibians and three Vickers Vildebeest torpedo-reconnaissance bombers, flown and serviced by seven officers and 108 airmen, was expanded to three hundred Hawker Tempests and fifty Newton Elephants. Now facing a large air assault, and with the possibility of air support arriving completely diminished, as the nearest fully operational RAF base was located in Kota Bharu, Malaya, nearly 2,250 kilometres away and unable to aid the city's defenders, the British air fleet of Hong Kong was ready to be tested for the first time on its own. While the city of Hong Kong had a decently sized air fleet defending it, its naval defences were lacking, allowing the Japanese to potentially strike from the sea.

As the battle began the Japanese bombed Kai Tak Airport destroying a few of the defending bombers on the ground. The attack also destroyed several civil aircraft including all but two of the aircraft used by the Air Unit of the Hong Kong Volunteer Defence Corp, forcing the RAF and Air Unit personnel from then on to fight as ground units. Two of the Royal Navy's three remaining destroyers were ordered to leave Hong Kong for Singapore. Only one destroyer, the HMS Thracian, several gunboats and a flotilla of motor torpedo boats remained.

The Commonwealth forces decided against holding the Sham Chun River and instead positioned their forces further back, establishing three battalions in the Gin Drinkers' Line across the hills. With no defense there the Japanese 38th Infantry under the command of Major General Takaishi Sakai quickly forded across the Sham Chun River by using temporary bridges, ready to meet the main force. Fighting began when the 228th Infantry Regiment, commanded by Colonel Teihichi, of the 38th Division attacked the Commonwealth defences at the Shing Mun Redoubt, controlled by the 2nd Battalion Royal Scots, under the command of Lieutenant Colonel S. White.

The 2nd Battalion Royal Scots held out against the aggressive Japanese attackers for five hours, before being forced to withdraw from their position of Golden Hill. This position was later retaken after a counterattack led by D company of the Toyal Scots. The hill soon fell again to the Japanese after another large wave of attack.

Overhead the British and Japanese engaged in a lofty, tense dog fight, as the Hong Kong Air Fleet met with the attacking fighters. The Newton Elephants under command of the British suffered heavy casualties against the more maneuverable Japanese fighters, although the Japanese were unable to completely break the British. As such the British were able to sparsely utilize bombers to aid their ground forces' advances.

With the aid of supporting air forces the British launched a series of attacks against Golden Hill, to varying success. Unable to completely push back the Japanese, the city now stood at risk. Under heavy artillery barrage the British began evacuating to Hong Kong island. By 20 December the British had almost completely abandoned the mainland, destroying military and harbour facilities in the withdrawal. The 5/7 Rajputs of the British Indian Army commanded by Lieutenant Colonel R. Cadogan-Rawlinson, the last Commonwealth troops on the mainland, held off the Japanese during the withdraw before falling back to the island later that day.

The defense of the island was left to Maltby, who split the island between an East Brigade and a West Brigade. After two attempts to force surrender from the British and constant bombardment of the North Shore, the Japanese forces launched their assault on the island, crossing the harbor and making land fall at the island's north-east coast. A series of light skirmishes ensued, costing the Japanese light casualties as they advanced.

By the next day fierce fighting had broken out across the island, leading to the Japanese annihilating the headquarters of West Brigade, causing the death of its commander, Brigadier John K. Lawson. The British launched a counterattack to attempt to force the Japanese from the Wong Nai Chung Gap that secured the passage between the north coast at Causeway Bay and the secluded southern parts of the island. The island became split in two with the British Commonwealth forces still holding out around the Stanley peninsula and in the West of the island. At the same time, water supplies started to run short as the Japanese captured the island's reservoirs.

By the afternoon of 1 January it had become clear that further resistance would be futile, and the British colonial officials headed by the Governor of Hong Kong, Sir Mark Aitchison Young, surrendered in person to the Japanese. This day would later become known in Hong Kong as "Black New Year's".

After the surrender the British became fully aware of the atrocities the Japanese had committed during the battle. Approximately 20 gunners were executed at the Sai Wan Battery despite having surrendered, while similar massacre of prisoners occured at the Salesian Mission on Chai Wan Road. The Japanese soldiers who entered the British field hospital at St. Stephen's College would also be discovered to have tortured and killed a large number of injured soldiers, along with the medical staff.

Following the surrender the Japanese began a period of occupation, appointing Isogai Rensuke as the first Japanese governor of Hong Kong. During this time Japanese soldiers terrorized the local population by murdering many, raping an estimated 10,000 women, and looting the city.

Invasion of Thailand
As Japanese forces began their assault on Pearl Harbor, Hong Kong, and other allied positions, the Japanese sought to begin an invasion of Malaya and Burma. In order to do this, the Japanese would need to utilize Thai ports, railways, and airfields, operating as a springboard into the rest of Southwest Asia. Japanese attempts to negotiate an agreement with Thai Prime Minister Phibun Songkhram, in which the Japanese military sought free passage through Thailand, ended with uncertainty, and acted to further warn the British of a potential attack looming against their possessions in Southeast Asia.

Although the Thai had a well disciplined army, experienced following the 1938 invasion of Indochina, Phibun could have considered he had little choice, as his own forces would have been unable to defeat the Japanese alone. Thailand's aggression against French Indo-China in 1940 also made it difficult for the United States government to support Phibun.

The Japanese invasion was launched on 13 December 1938. Japanese troops invaded Thailand from Indo-China, landings soldiers south of Bangkok and at various points along the Kra Peninsula. At the time of the invasion the Thai government was unable to contact Songkhram, their Prime Minister. The Japanese invasion force was divided between the 15th and 25th armies, with each in charge of a different set of objectives.

Following the initial attack, the Imperial Japanese Army 33rd Division under Lieutenant-General Shōzō Sakurai and the Imperial Japanese Army 55th Division under Lieutenant-General Hiroshi Takeuchi of the 15th Army, spearheaded by the Imperial Guards Division, crossed the border from Indo-China into Thailand's recently reclaimed Phra Tabong Province at Tambon Savay Donkeo, Athuek Thewadej District (Russei) of Battambang. The Japanese encountered no resistance in this area, and from Sisophon swung north-westwards into Aranyaprathet, which remained still a district of Prachinburi Province at the time, along the finished railway link between Aranyaprathet and Monkhol Bourei.

The Japanese 1st Infantry Battalion of the 143rd Infantry Regiment, part of the Imperial Japanese Army 55th Division, landed at Chumphon. After forming a small perimeter around their landing site they became pinned down by determined resistance, consisting of the the 52nd Youth Army Training Unit from Sriyaphai School and the 38th Infantry Battalion and Provincial Police of Chumpon. During the fighting Thai Captain Thawin Niyomsen was killed, as was several provincial police and a few civilians.

Another Japanese landing would take place at Nakhon Si Thammarat, the site of the Thai Sixth Army Division’s Headquarters and 39th Infantry Battalion. Three Japanese troopships, Zenyo, Miike and Toho Maru's, land troops at Nakorn Sri Thammarat, S Siam, covered by the Shimushu, dropping anchor a few kilometres off the coast during the night of December 10. The invading force of 1,510 men and 50 trucks of the 3rd Infantry Battalion of the 143rd Infantry Regiment, the 18th Air District Regiment along with an army air force signals unit, the 32nd Anti-Aircraft Battalion, and the 6th Labour Construction Company, began disembarking their troops at the Tha Phae canal (also known as Pak Phoon Canal), North of Camp Vajiravudh, to which the landing was made adjacent. Receiving news of the invasion at Songkhla, the Thai forces immediately went into action, fighting until the end of the invasion.

Similar invasions would be launched across southern Thailand, supported by air craft overhead who worked to bomb major cities and strategic positions. Plaek Pibulsonggram finally made the decision to sign an armistice with Japan effectively ending any chance of Thailand joining the allied forces. He also granted Japan permission to use Thailand as a base of operations to invade Malaya. Within hours after the armistice came into effect, squadrons of Japanese aircraft had flown into Songkla airfield from Indochina, allowing them to carry out air raids on strategic bases in Malaya and Singapore from a short distance. At the time of the ceasefire, Britain and the United States regarded Thailand as Japanese-occupied territory.

Malayan Campaign
The Japanese would launch the Invasion of Malaya just after midnight on 13 December 1938 (local time) before the attack on Pearl Harbor. It was the first major battle of the Pacific War, and was fought between ground forces of the British Indian Army and the Empire of Japan. The Royal Air Force's (RAF) and Royal Australian Air Force's (RAAF) base of operations in Northern Malaya, Kota Bharu, capital of Kelantan State on Malaysia's northeast coast, served as an important site in the defense of the region, utilizing an airstrip at Kota Bharu and two more at Gong Kedah and Machang. Sporadic Australian air attacks, Indian coastal defences, and artillery fire would help to delay the Japanese invasion.

Invasion of Malaya
The Japanese invasion of Malaya was planned to involve landing troops from the 5th Division at Pattani and Songkhla on Thailand's east coast, and troops from the 18th Division at Kota Bharu Malaya's northeast coast. The forces in Thailand were to push through to the west coast and invade Malaya from the northwestern province of Kedah, while the eastern forces would attack down the east coast and into the interior of Malaya from Kota Bharu. Following the successful Japanese invasion of Thailand an invasion of Malaya was considered possible.

The British planned to defend against an invasion from Thailand into northwestern Malaya by launching a pre-emptive strike into southern Thailand, known as Operation Krohcol, in order to take strategically vital positions and delay the enemy attack. Along the eastern coast the British mounted fixed beach defenses, manned by the Indian 9th Infantry Division along the northern stretch of coastline and two thirds of the Australian 8th Division, with the other third being on Ambon, West Timor, and at Rabaul, defending the southern stretch of coastline.

Japanese forces from the 25th Army under Lieutenant General Tomoyuki Yamashita were moved from Samah Harbour on Hainan Island to positions near Malaya, ready to invade following the outbreak of war. Additional forces met the convoy from Saigon in southern Vietnam, French Indochina.

Malayan Peninsula
By the outbreak of war British defenses had been concentrated at several key points, including Jitra, where barbed wire lines, anti-tank mines, trenches, and gun pits surrounded the city. Reinforced telephone cables had been established in the late 1940's after the initial lines laid across the waterlogged ground failed to work, allowing for quick and relatively reliable communication down the Malay Peninsula.

The front line was placed under the command of Major General David Murray-Lyon and the 11th Indian Division. The right flank was held by the 15th Indian Infantry Brigade, composed of 1st Leicestershires, the 1/14th Punjab Regiment and the 2/9th Jats, while the left flank was held by the 6th Indian Infantry Brigade, composed of the 2nd East Surreys, the 1/8th and 2/16th Punjab Regiments. Batteries from the 155th Field Regiment, the 22nd Mountain Regiment and the 80th Anti-tank Regiment provided the artillery support. A third brigade—the 28th Indian Infantry Brigade, consisting of three Gurkha battalions—was placed in divisional reserve.

After Operation Matador a full-scale preemptive strike into Thailand was canceled, and the British fell back, holding a fourteen mile long front, stretching across both roads and a railway, and far beyond on either side, from the jungle-clad hills on the right via flooded rice fields and a rubber estate to a tidal mangrove swamp on the left. The 11th Indian Division moved back forming defensive positions around Jitra.

The 5th Infantry Division under Takuma Nishimura advanced on Jitra, engaging the British defenses outside the city. Equally matched the British were able to hold back the Japanese for several days, holding against constant bombardment. The Japanese advance guard overran a forward patrol of the 1st Leicesters but was held up by an improvised roadblock. Believing he was still attacking small British delaying forces launched his men into a three-hour attack on the Leicesters and Jat positions without success.

Realizing they were fighting against the main 11th Indian Division positions, General Kawamura, commanding the Imperial Japanese Army's 9th Brigade, placed the 11th and 41st Infantry Regiments in readiness to resume the attack that night.

Dutch East Indies Campaign
The strength of the combined navies of the Allied nations became crucial to the war against Japan. Following the Japanese attack on the Republic of Hawaii's naval dock; Pearl Harbor, the nation of Hawaii and other United States remnant nations placed sole command of their naval forces in the hands of the British and Dutch naval command, combining units from Alaska, Hawaii, the Philippines, and United States Far East bases and outposts.

This combined naval effort would play an important part in the war against Japan. Given the great vastness of sea between the various islands and regions of the Pacific Ocean, the placement of the Allied power's concentrated fleets was a key consideration in military tactics.

Both sides of the war had begun to consider and recognize the increasingly important role the aircraft carrier played in emerging naval tactics, with both sides investing greatly in the ship's technology. The aircraft carrier was becoming increasingly significant to naval warfare quite simply because of the weapons that it supported, including the easy deployment of bombers and other aircraft at a naval target. Bomber aircraft was becoming increasingly more accurate, and they could be used to strike and hit a variety of targets, including naval ships such as battleships and indeed other aircraft carriers. With such aircraft, the range of the aircraft carrier comfortably exceeded other naval ships and could be used to support both naval and ground battles.

Makassar Strait
By early 1939 the Japanese forces had managed to seize large portions of the north and west coast of Borneo and large parts of Maluku (Moluccas). The Japanese forces occupied the oil facilities and ports of the Balikpapan and Tarakan, on Borneo's west coast. The cities of Menado and Kendari on Celebes also fell to Japanese forces.

Allied forces received word from a reconnaissance plane on 1 February that at Balikpapan a Japanese invasion force consisting of twenty troop transport ships, three cruisers, and ten destroyers was preparing to sail. The next naval leaders of the Dutch East Indies and Unites States Remnant navy met in the city of Palembang to create a plan for their next move. The idea of a strike force being formed was approved, and was formed the following day to begin sending supplies from the Gili Islands, south of Madura.

At the time of its creation the strike group consisted of the USS Barker, a Clemson-class destroyer from the United States remnant fleet stationed in Borneo at the time of the eruption, and under the command of the Dutch navy, the USS Bulmer and the USS John D Edwards, former US ships from the Philippines, the HNLMS De Ruyter, HNLMS Banckert, HNLMS Piet Hein, HLNMS Van Ghent, and the fleet's flagship; the HNLMS Tromp, all provided from the Dutch command in the Dutch East Indies, and lastly the USS Detroit, a survivor of the attack on Pearl Harbor. After surviving the attack and returning to Pearl Harbor after investigating he west coast of Oahu for any indications of a landing by the Japanese, the USS Detroit began convoy escort duty and good transport between the west coast and Hawaii. This operation was cut short to move the hastily move the ship to the Dutch East Indies.

The strike group was spotted by a squadron of about thirty Japanese bombers heading toward Surabaya on 3 February. The Allied ships responded by dispersing to deeper water, but why then the Japanese aircraft had left without attacking, leaving the group to resume taking supplies. At about midnight the ships sailed for Meinderts Droogte (Meinderts Reef; later Karang Mas), off the north east tip of Java. With the last ship in the group arriving on 4 February at five o'clock, the force received word at 09:30 that air patrols from Makassar had spotted the Japanese heading for Surabaya. That morning the Allied strike group departed for Makassar Strait in search of the Japanese invasion force, which was reported to be passing through the straits and was now said to include three cruisers and eighteen destroyers, escorting transports and other ships, under Sho-sho (Rear Admiral) Takeo Takagi. Japanese bombers were spotted to the east by Allied sailors aboard the fleet, just as the group reached the south of the Kangean Islands. It was reported that at this time the Japanese planes had begun flying in four "v"-formations, maintaining an altitude of about 16,404 ft (5,000 m).

The battle begin with the Japanese planes' assault of the Allied cruisers. The first to be targeted was the USS Detroit, and the bombs landed about 262 ft (80 m) in front of the ship. During a second attack, Detroit sustained two direct hits and a damaging near miss. The two direct hits penetrated the deck, killed 15 crew directly and destroyed the ship's ability to maneuver, leaving Detroit now able only to sail in circles. The near miss also caused a hole three by one meters near the bottom of the ship, however, subsequent attacks on Detroit were less intense. USS Barker initially evaded bombs successfully, but suffered a severe hit during a final attack, with two bombs hitting the deck near the aft gun turret, killing 71 crew members. The attack also rendered the rear guns useless.

After the hits on Detroit and Barker, the planes focused on De Ruyter, which evaded four attacks and sustained only minor damage to fire control for its 40 mm guns. The HNLMS Piet Hein and HNLMS Banckert were also briefly targeted, with the Piet Hein being hit by a single direct hit bomb, killing 38 crewmen. After hours of fighting, the Dutch command finally ordered the strike group to withdraw at about 13:00, with the group being ordered to return west, believing that without proper protection from bombers it would not be possible to advance to Makassar Strait. Barker and Tromp had already gone south through Alas Strait, and were south of the strait. Detroit and the several destroyers went south through Lombok Strait. De Ruyter and the Dutch destroyers also stayed with Detroit until the Lombok Strait. Several cruisers headed for Tjilatjap, to get repairs and medical attention for their wounded.

After the engagement Japanese aircrews reported the sinking of three cruisers, including one Augusta class cruiser (the Northampton-class), one Tromp-class cruiser type and one Java-class cruiser. In reality no ships of the latter class were present during the attack, and the only ships to be damaged were the Detroit, Barker, and Piet Hein. At Tjilatjap wounded crewmen were transferred to a hospital, while the dead were buried there. Detroit was unable to fit in the dry dock, but the hole in the hull was temporarily repaired, allowing the ship to sail south for repairs. The USS Barker would continue serving in the Allied strike group. The retreat of the strike force resulted in the Japanese taking control of Makassar Strait and thereby tightening their grip on the western part of the Dutch East Indies.

Badung Strait
On 18 February 1939 a battalion of the 48th Infantry Division of the Imperial Japanese Army landed on Bali, giving the Japanese an airbase within range of the crucial Allied naval base at Surabaya. Dutch Admiral Karel Doorman's naval forces were scattered around the Dutch East Indies, but could not ignore the threat the Japanese imposed. All available ships were sent but the short notice gave the Allied forces no time to concentrate their forces. The Japanese convoy was observed by Allied submarines, but were unable to do any damage and were driven off by depth charges from Japanese destroyers. Later that day, twenty American fighters attacked the convoy but succeeded only in damaging the transport Sagami Maru.

Aware that the convoy would likely be attacked again, the Japanese convoy quickly retreated north. The cruiser Nagara and the destroyers Wakaba, Hatsushimo and Nenohi were well away and were able to easily withdraw, taking no part in the action. The last ships to leave were the two transports, each escorted by two destroyers. Sasago Maru was escorted by Asashio and Oshio; the heavily damaged Sagami Maru was escorted by Michishio and Arashio. The first Allied group, consisting of the cruisers HNLMS De Ruyter and Java, and the destroyers USS John D. Ford, Pope, and HNLMS Piet Hein, sighted the Japanese in Badung Strait on 19 February at about 22:00, and opened fire at 22:25. In the initial exchange no damage was done, and the two Dutch cruisers continued through the strait to the northeast, to give the destroyers a free hand to engage with torpedoes. With the Piet Hein, Pope and John D. Ford now coming into range, at 22:40, a Long Lance torpedo from Asashio hit Piet Hein, sinking the Dutch destroyer immediately. Asashio and Oshio then exchanged gunfire with Pope and John D. Ford, forcing the two American destroyers to retire to the southeast instead of following the cruisers to the northeast. In the darkness, Asashio and Oshio mistook each other for enemy ships and fired on each other for several minutes, without any damage.

About three hours later, the second group of Allied ships, consisting of the cruiser HNLMS Tromp and the destroyers USS John D. Edwards, Parrott, Pillsbury, and Stewart, reached Badung Strait. At 01:36, Stewart, Pillsbury and Parrott launched torpedoes but did no damage. Oshio and Asashio sortied again and there was another exchange of gunfire. Tromp was hit by eleven 5 in (130 mm) shells from Asashio, severely damaging her, but hit both Japanese destroyers, killing four men on Asashio and seven on Oshio. Tromp later had to return to Australia for repairs. Arashio and Michishio had been ordered by Admiral Kubo to turn back, and at about 02:20 they joined the battle. Michishio was hit by shells from Pillsbury, John D. Edwards and Tromp, killing 13 of her crew and wounding 83. She lost speed and had to be towed after the battle. Both groups of ships turned away, and the engagement was over.

After the battle's conclusion the third Allied group arrived, consisting of seven torpedo boats, entering the Badung Strait at about 06:00, but did not encounter any Japanese ships. The battle was a significant victory for the Japanese. Lieutenant Commander Gorō Yoshii of Asashio and Commander Kiyoshi Kikkawa of Oshio had shown great bravery and skill, and were praised for driving off such a much larger Allied force. The Japanese had successfully sunk the destroyer Piet Hein and severely damaged the cruiser Tromp, sustaining little damage themselves, and had protected their transport ships.

Bali's garrison of 600 Indonesian militia offered no resistance to the Japanese, and its airfield was captured intact. The Japanese continued their conquest of the Dutch East Indies with the capture of Timor from 20 to 23 February. The Allied forces engaged at Badung Strait were decisively defeated in the Battle of the Java Sea on 1 March 1942, in which the Dutch cruisers Java and De Ruyter were sunk and Admiral Doorman was killed. Tromp evaded this fate, for she was withdrawn to Australia to repair damage suffered at Badung Strait. The destroyer Stewart was repaired in Soerabaia, where she was next captured by the Japanese and put to their service as the patrol vessel P-102.

Java Sea
On land the Japanese army had managed to successfully invade and occupy the Palau Islands colony, captured bases in Sarawak and the southern Philippines, and had advanced to seize bases in eastern Borneo and in northern Celebes. The advance was aided by swarms of fighters operating from captured bases, steamed southward through the Makassar Strait and into the Molucca Sea. The small naval force of Dutch, American, British & Australian warships, stood to oppose them, although heavily outnumbered and outgunned.

On 23 January 1939, a force of four American destroyers attacked a Japanese invasion convoy in Makassar Strait as it approached Balikpapan in Borneo. On 13 February, the Allies fought unsuccessfully in the Battle of Palembang to prevent the Japanese from capturing the major oil port in eastern Sumatra. On the night of 19/20 February, an Allied force attacked the Eastern Invasion Force off Bali in the Battle of Badung Strait. Also on the 19th, the Japanese made two air raids on Darwin, one from carrier based planes and the other by land based planes. The destruction of Darwin rendered it useless as a supply and naval base to support operations in the East Indies.

The odds were not good for the Allied forces, who were left disorganized and demoralized. They were disunited and spread thin, with ships being provided from nations all around the Pacific. Many ships began to be demoralized by constant air attacks, and a general sentiment that the Japanese were unbeatable. In addition, the coordination between Allied navies and air forces was poor.

By late February Japanese amphibious forces had gathered to strike at Java, and on 27 February 1942, the main Allied naval force, under Doorman, sailed northeast from Surabaya to intercept a convoy of the Eastern Invasion Force approaching from the Makassar Strait. The Allied force consisted of the British heavy cruiser; the HMS Exeter, and the light cruisers HMS Electra, transferred from the Mediterranean Sea, the HMAS Perth, the USS Alden transferred from the Hawaiian remnant fleet at Pearl Harbor, the USS John D. Ford, USS Paul Jones, and USS Parrott, transferred from the Philippines, and the HNLMS Kortenaer, HNLMS Witte de With, and the USS John D Edwards, veterans of the Battle of Makassar Strait a few weeks earlier.

The approaching Japanese task force protecting the convoy was under the command of Rear-Admiral Takeo Takagi, and consisted of the Nachi and Haguro heavy cruisers, Naka and Jintsu light cruisers, and the Yudachi, Samidare, Murasame, Harusame, Minegumo, Asagumo, Yukikaze, Tokitsukaze, Amatsukaze, Hatsukaze, Yamakaze, Kawakaze, Sazanami, and Ushio destroyers, including the 4th Destroyer Squadron under the command of Rear Admiral Shoji Nishimura. The Japanese heavy cruisers were also much more powerful, armed with ten 8 in (200 mm) guns each and superb torpedoes. By comparison, Exeter was armed only with six 8 in (200 mm) guns. While Houston carried nine 8 in (200 mm) guns, only six remained operable after her aft turret had been knocked out in an earlier air attack.

The Battle of the Java Sea begin with Allied forces engaging the Japanese navy. The battle soon raged on long into the night, with the Allies many attempts to reach and attack the troop transports of the Java invasion fleet, but were repeatedly pushed back by the Japanese navy's superior weaponry. During the daylight hours the Allies maintained local air superiority, because Japanese air power could not reach the fleet in the bad weather, but the weather also hindered communications, making cooperation between the many Allied parties involved in reconnaissance, air cover and fleet headquarters even worse than it already was. Radio frequencies were also jammed by the Japanese.

The battle consisted of a series of attempts over a seven-hour period by Doorman's Combined Striking Force to reach and attack the invasion convoy; each was rebuffed by the escort force with heavy losses being inflicted on the Allies. At about 16:00 on 27 February the fleets sighted each other and closed to firing range, opening fire at 16:16. Both sides exhibited poor gunnery and torpedo skills during this phase of the battle. Despite her recent refit (with the addition of modern Type-284 gunery control radar), Exeter's gun-fire did not come close to the Japanese ships. During the exhange the Exeter was critically damaged by a direct hit on its boiler room from an 8 in (200 mm) shell. Exeter, escorted by the Witte de With, retreated to Surabaya.

The Japanese followed up by launching two huge torpedo salvoes, 92 in all, on the Allied position, but scored only one hit, on Kortenaer, who was broken in two and sank rapidly after the hit. Electra engaged in a duel with Jintsu and Asagumo while simultaneously protecting Exeter's withdraw. During the engagement Electra managed to score several hits but suffered severe damage to her superstructure. After a serious fire started on Electra and her remaining turret ran out of ammunition, abandon ship was ordered. On the Japanese side, only Asagumo was forced to retire because of damage.

A loose smoke screen was laid by some of the American remnant destroyers, who covered the Allied retreat as they broke off and fled. A torpedo attack was launched in the chaos, but was too far away to be effective. Doorman's force turned south toward the Java coast, then west and north as night fell in an attempt to evade the Japanese escort group and fall on the convoy. It was at this point the American destroyers, out of torpedoes and working on their own initiative, chose to return to Surabaya.

Shortly after, at 21:25, Jupiter ran onto a mine and was sunk, while about 20 minutes later, the fleet passed where Kortenaer had sunk earlier, and Encounter was detached to pick up survivors. Doorman's command, now reduced to four cruisers, again encountered the Japanese escort group at 23:00. Both columns exchanged fire in the darkness at long range, until a single torpedo salvo managed to sink both De Ruyter and Java. Doorman and most of his crew went down with De Ruyter; only 111 were saved from both ships. Only the cruisers Perth and Parrott remained. Now low on fuel and ammunition, and following Doorman's last instructions, the two ships retired, arriving at Tanjung Priok on 28 February. Although the Allied fleet did not reach the invasion fleet, the battle did give the defenders of Java a one-day respite.

Invasion of Java
With the Allied fleet defeated and failing to stop the advancing Japanese convoy, the Japanese reached the island of Java by the end of February 1939. The Japanese landed troops at three points on Java on 1 March. The West Java invasion convoy, which had previously fought in the Battle of Sunda Strait a few hours prior, landed on Bantam Bay near Merak and Eretan Wetan. The East Java invasion convoy landed on Kragan after having defeated the Allied fleet in the Battle of the Java Sea. Once on the ground the Japanese forces were split into two groups: the Eastern Force, with its headquarters at Jolo Island in the Sulu Archipelago, included the 48th Division and the 56th Regimental Group, and the Western Force, based at Cam Ranh Bay, French Indochina, including the 2nd Division and the 230th Regiment detached from the 38th Division.

Fighting in the defense of Java, the Allied forces were commanded by the Royal Netherlands East Indies Army (KNIL) commander, General Hein ter Poorten. Although the KNIL was documented to have about 25,000 well-armed troops, mostly originating from Indonesia, many were in fact poorly or hastily trained. The KNIL forces were deployed in four sub-commands: Batavia (Jakarta) area (two regiments); north central Java (one regiment); south Java (one regiment) and; east Java, one regiment.

British Major General H. D. W. Sitwell was placed in command of he British, Australian and American units. The British forces, who were predominantly anti-aircraft units, consisted of the 77th Heavy AA Regiment, 21st Light AA Regiment and 48th Light AA Regiment. The only British armoured unit on Java was a squadron of light tanks from the British 3rd Hussars. Two British AA regiments without guns, the 6th Heavy AA Regt and the 35th Light AA Regiment were equipped as infantry to defend airfields. The British also had transport and administrative units.

The Australian formation, named "Blackforce" after its commander, Brigadier Arthur Blackburn V.C., included the Australian 2/3rd Machine Gun Battalion, the Australian 2/2nd Pioneer Battalion, a company from the Royal Australian Engineers, a platoon from the 2/1st Headquarters Guard Battalion, about 100 reinforcements diverted en route to Singapore, a handful of soldiers who had escaped from Singapore following its fall to the Japanese, two transport companies, a casualty clearing station, and a company headquarters unit. Blackburn decided to reorganize his troops as an infantry brigade. They were well-equipped in terms of Bren guns, light armored cars, and trucks, but they had few rifles, sub machine guns, anti-tank rifles, mortars, grenades, radio equipment or Bren gun carriers. Blackburn managed to assemble an HQ staff and three infantry battalions based on the 2/3rd Machine Gun, the 2/2nd Pioneers, and a mixed "Reserve Group".

Lieutenant General Hitoshi Imamura received an order to attack Java on 30 January after discussing the war preparation with the commander of the 3rd Fleet and inspecting the 48th Division at Manila a little more than a week earlier. His convoy consisted of 56 transport ships with troops aboard from the 16th Army Headquarters, 2nd Division and 230th Infantry Regiment. The convoy left Cam Ranh Bay at 10:00 on 18 February, and the commander-in-chief Lieutenant General Hitoshi Imamura was aboard on the transport ship Ryujo Maru. The convoy escort was under the command of Rear Admiral Kenzaburo Hara.

On 28 February at 23:20 the transport ships carrying the Nasu and Fukushima detachments commenced landing operations at Merak. Ten minutes later they were joined by the other transport ships, including the one carrying the Sato detachment, which dropped anchor at Bantam Bay. By 02:00 on 1 March, all ships had reached their designated positions.

Operation MO and Tulagi
With the Dutch East Indies falling to the Japanese forces from the north, the allies now stood exhausted and ill supplied. The Allies had also suffered heavy casualties in terms of land, naval, and aircraft loses, weakening their chance of a successful counterattack against the new well defended Japanese Armed Forces. Japan planned in the next few months to establish a defensive perimeter around its occupied territory, reaching from Burma and Malaya in Southeast Asia, running through the Dutch East Indies, and traveling north of Australia, expecting to deploy attritional tactics to defeat or exhaust any Allied counterattacks.

The Japanese Naval General Staff recommended an invasion of Northern Australia in early 1942, hoping to prevent Australia from being used as a base of operations to threaten the Japanese perimeter in the South Pacific. The plan was however rejected by the Imperial Japanese Army, who deemed that at the time the Japanese did not have the necessary forces or shipping capacity available to conduct such an operation. A second plan by Vice Admiral Shigeyoshi Inoue, commander of the IJN's 4th Fleet (also called the South Seas Force), advocated for the occupation of Tulagi in the southeastern Solomon Islands and Port Moresby in New Guinea, which would put northern Australia within range of Japanese land-based aircraft.

The Japanese submarines RO-33 and RO-34 were sent to reconnoiter the possible landing sites on New Guinea, observing Rossel Island and the Deboyne Group anchorage in the Louisiade Archipelago, Jomard Channel, and the route to Port Moresby from the east. The two submarines independently retrned to Rabaul on 23 and 24 April respectively after not sighting any Allied ships in the area.

Proceeding with the invasion plan, the Japanese Port Moresby Invasion Force, commanded by Rear Admiral Kōsō Abe, was created. The invasion force included eleven transport ships carrying about 5,000 soldiers from the IJA's South Seas Detachment plus approximately 500 troops from the 3rd Kure Special Naval Landing Force (SNLF). Escorting the transports was the Port Moresby Attack Force with one light cruiser and six destroyers under the command of Rear Admiral Sadamichi Kajioka. Abe's ships departed Rabaul for the 840 nmi (970 mi; 1,560 km) trip to Port Moresby on 4 May and were joined by Kajioka's force the next day. The ships, proceeding at 8 kn (9.2 mph; 15 km/h), planned to transit the Jomard Channel in the Louisiades to pass around the southern tip of New Guinea to arrive at Port Moresby by 10 May.

The invasion of Tulagi was lead by the Tulagi Invasion Force, commanded by Rear Admiral Kiyohide Shima, and consisted of two minelayers, two destroyers, six minesweepers, two subchasers, and a transport ship carrying about 400 troops from the 3rd Kure SNLF. The Tulagu firce was supported Supporting the Tulagi force was the Covering Group with the light carrier Shōhō, four heavy cruisers, and one destroyer, commanded by Rear Admiral Aritomo Gotō. A separate Cover Force (sometimes referred to as the Support Group), commanded by Rear Admiral Kuninori Marumo and consisting of two light cruisers, the seaplane tender Kamikawa Maru, and three gunboats, joined the Covering Group in providing distant protection for the Tulagi invasion. Once Tulagi was secured on 3 or 4 May, the Covering Group and Cover Force were to reposition to help screen the Port Moresby invasion. Inoue directed the MO operation from the cruiser Kashima, with which he arrived at Rabaul from Truk on 4 May.

Gotō's force left Truk on 28 April, cut through the Solomons between Bougainville and Choiseul and took station near New Georgia Island. Marumo's support group sortied from New Ireland on 29 April headed for Thousand Ships Bay, Santa Isabel Island, to establish a seaplane base on 2 May to support the Tulagi assault. Shima's invasion force departed Rabaul on 30 April.

The Carrier Strike Force with carriers Zuikaku and Shōkaku, two heavy cruisers, and six destroyers sortied from Truk on 1 May. The strike force was commanded by Vice Admiral Takeo Takagi (flag on cruiser Myoko) with Rear Admiral Chūichi Hara, on Zuikaku, in tactical command of the carrier air forces. The Carrier Strike Force was to proceed down the eastern side of the Solomon Islands and enter the Coral Sea south of Guadalcanal. Once in the Coral Sea, the carriers were to provide air cover for the invasion forces, eliminate Allied air power at Port Moresby, and intercept and destroy any Allied naval forces which entered the Coral Sea in response.

En route to the Coral Sea, Takagi's carriers were to deliver nine Zero fighter aircraft to Rabaul. Bad weather during two attempts to make the delivery on 2–3 May compelled the aircraft to return to the carriers, stationed 240 nmi (280 mi; 440 km) from Rabaul, and one of the Zeros was forced to ditch in the ocean. In order to try to keep to the MO timetable, Takagi was forced to abandon the delivery mission after the second attempt and directed his force towards the Solomon Islands to refuel.

To give advance warning of the approach of any Allied naval forces, the Japanese sent submarines I-22, I-24, I-28 and I-29 to form a scouting line in the ocean about 450 nmi (520 mi; 830 km) southwest of Guadalcanal. Unknown to the Japanese the Allies had managed to pass into the Coral Sea area before the submarines took station, and the Japanese were therefore unaware of their presence. Another submarine, I-21, which was sent to scout around Nouméa, was attacked by the USS Ranger's aircraft on 2 May. The submarine took no damage and apparently did not realize that it was attacked by carrier aircraft. RO-33 and RO-34 were also deployed in an attempt to blockade Port Moresby, and arrived off the town on 5 May. Neither submarine engaged any ships during the battle.

With the Japanese army and navy approaching Port Moresby the garrison there had no choice but to attempt a defense. In comparison to the elaborate Japanese invasion force the Allied garrison at Port Moresby numbered around 5,333 men, but only half of these were infantry and all were badly equipped and under trained.

Battle of the Coral Sea
On the morning of 7 May the cruiser and destroyer force under the command of Australian commander John Gregory Crace, now designated as Task Group 17.3, was ordered by Allied commander Frank Jack Fletcher to block the Jomard Passage. Knowing that Crace would be operating without air cover, since the Allied carriers would be busy engaging the Japanese carriers, Fletcher decided that the risk was necessary in order to ensure that the Japanese invasion forces could not slip through to Port Moresby while he was engaged with the Japanese carriers.

Believing Takagi's carrier force was somewhere north of his location, in the vicinity of the Louisiades, Fletcher directed Ranger to send ten SBD dive bombers as scouts to search that area. At the same time, located about 300 nmi wast of Fletcher, Takagi launched twelve type 97 carrier bombers to scout for Ranger's task force. Gotō's cruisers Kinugasa and Furutaka launched four Kawanishi E7K2 Type 94 floatplanes to search southeast of the Louisiades. Augmenting their search were several floatplanes from Deboyne, four Kawanishi Type 97s from Tulagi, and three Mitsubishi Type 1 bombers from Rabaul. Each side readied the rest of its carrier attack aircraft to launch immediately once the enemy was located.

A little more than an hour later a scout from one of Takagi’s carriers, the Shōkaku, sighted and located the American ships, bearing 182°, 163 nmi (188 mi; 302 km) from Takagi’s position., and reported the sighting to the Japanese command. The sighting was later confirmed by a second scout from the Shōkaku, confirming the sighting of "one carrier, one cruiser, and three destroyers". What the Japanese scouts interpreted as a carrier and its support ships was actually two misidentified Allied destroyers. Hara, with Takagi's concurrence, immediately launched all of his available aircraft, reaching a total of seventy eight aircraft, including eighteen Zero fighters, thirty six Type 99 dive bombers, and twenty four torpedo aircraft, launched from Shōkaku and Zuikaku , which rbegan approaching the Allied positionj within fifteen minutes.

A few minutes later a Furutaka aircraft located Fletcher's carriers and immediately reported it to Inoue's headquarters at Rabaul, which passed the report on to Takagi. The sighting was confirmed by a Kinugasa floatplane soon after. Takagi and Hara, confused by the conflicting sighting reports they were receiving, decided to continue with the strike on the ships to their south, but turned their carriers towards the northwest to close the distance with Furutaka's reported contact. Takagi and Hara considered that the conflicting reports might mean that the American carrier forces were operating in two separate groups.

Gotō's force were sighted by an Allied pilot screening the invasion convoy, and reported their presence. Fletcher concluded that the Japanese main force had been located, and ordered the launch of all available carrier aircraft to attack. Shortly after the order, a combined force of ninety three aircraft, including eighteen F4F Wildcats, fifty three SBD dive bombers, and twenty two TBD Devastator torpedo bombers, was on its way to the Japanese position. Although Gotō's force included Shōhō, it was revealed to not be the entire force. Fletcher received a report of an aircraft carrier, ten transports, and sixteen warships 30 nmi (35 mi; 56 km) south of the earlier sighting. The second sighting would soon be revealed to be a similar collection to the first sighting, including the Shōhō, Gotō's cruisers, plus the Port Moresby Invasion Force. The Allied airborne strike force would later be directed towards this target.

When Takagi's strike force reached its target area they searched in vain for the Allied carriers. After an hour of searching the Shōkaku scout aircrews realized they were mistaken in their identification of the oiler and destroyer as aircraft carriers. Takagi now realized the American carriers were between him and the invasion convoy, placing the invasion forces in extreme danger. Takagi ordered his aircraft to immediately attack the sighted, mislabeled ships, and then return to their carriers as quickly as possible. After about an hour the torpedo bombers and fighters abandoned the mission and headed back towards the carriers with their ordnance while the thirty six dive bombers attacked the two Allied ships.

The destroyer was hit by three bombs, broke in half, and sank immediately, killing all but 14 of her 192-man crew. The second ship was hit by seven bombs. One of the dive bombers, hit by anti-aircraft fire, crashed into the oiler. Heavily damaged and without power, the second ship was left drifting and slowly sinking. Before losing power, the second ship was able to notify Fletcher by radio that she was under attack and in trouble, but garbled any further details as to just who or what was attacking her and gave wrong coordinates for its position.

At the same time the Allied strike aircraft sighted Shōhō a short distance northeast of Misima Island and deployed to attack. The Japanese carrier was protected by six Zeros and two Type 96 'Claude' fighters flying combat air patrol (CAP), as the rest of the carrier's aircraft were being prepared below decks for a strike against the Allied carriers. Gotō's cruisers surrounded the carrier in a diamond formation, 3,000–5,000 yd (2,700–4,600 m) off each of Shōhō's corners.

The USS Lexington's air group, led by Commander William B. Ault, opened fire on the Japanese first, hitting Shōhō with two 1,000 lb (450 kg) bombs and five torpedoes, causing severe damage. During the fighting Ranger's air group was targeted and heavily attacked, leaving its aircraft almost completely destroyed, and the carrier itself stationary, scoring with up to eleven more 1,000 lb (450 kg) bombs and at least two torpedoes. Torn apart, Shōhō sank from excessive Allied hits. Gotō withdrew his warships to the north fearing more air attacks, but sent the destroyer Sazanami back to rescue survivors. Only 203 of the carrier's 834-man crew were recovered. Three Allied aircraft were lost in the attack, including two SBDs from Lexington and one from Ranger. All of Shōhō's aircraft complement of eighteen was lost, but three of the CAP fighter pilots were able to ditch at Deboyne and survived.

Following the engagement the Allied aircraft returned to their carriers and landed. Two hours after noon the Allied aircraft force was rearmed and ready to launch against the Port Moresby Invasion force and Gotō's cruisers. With the rest of the Japanese force still unknown, Fletcher was hesitant to devote the resources and ships to another attack so soon without further information. He was later informed that Allied intelligence sources believed that up to four Japanese carriers might be supporting the MO operation. Fletcher concluded that by the time his scout aircraft located the remaining Japanese carriers it would be too late in the day to mount a strike. Thus, Fletcher decided to hold off on another strike this day and remain concealed under the thick overcast with fighters ready in defense. Fletcher's task force TF17 was turned southwest.

Upon hearing of the loss of the Shōhō, Inoue ordered the invasion convoy to temporarily withdraw to the north, and ordered Takagi, at this time located 225 nmi (259 mi; 417 km) east of TF 17, to destroy the American carrier forces. As the invasion convoy reversed course to withdraw north, it was bombed by eight Allied bombers but was not damaged. Gotō and Kajioka were told to assemble their ships south of Rossel Island for a night surface battle if the Allied ships came within range.

Crace's force was sighted and reported by a Deboyne-based seaplane sighted and reported Crace's force bearing 175°, 78 nmi (90 mi; 144 km) from Deboyne.Later an aircraft from Rabaul sighted Crace's force but submitted an erroneous report, stating the force contained two carriers and was located bearing 205°, 115 nmi (213 km) from Deboyne. Based on these reports, Takagi, who was still awaiting the return of all of his aircraft from attacking the two confirmed ships, turned his carriers due west at and advised Inoue at that the Allied carriers were at least 430 nmi (490 mi; 800 km) west of his location and that he would therefore be unable to attack them that day.

Two groups of attack aircraft were directed by Inoue's staff from Rabaul, who were airborne since the morning earlier, to attack Crace's reported position. The first group consisted of twelve torpedo-armed Type 1 bombers, and the second group comprised nineteen Mitsubishi Type 96 land attack aircraft. Both groups found and attacked Crace's ships at soon after and claimed to have sunk a "California-type" battleship and damaged another battleship and cruiser. In reality, Crace's ships were undamaged and shot down four Type 1s. A short time later, three Allied bombers mistakenly bombed Crace, but caused no damage.

After the engagement Crace radioed Fletcher and informed him that he could not complete his mission without air support. Crace retired southward to a position about 220 nmi (250 mi; 410 km) southeast of Port Moresby to increase the range from Japanese carrier or land-based aircraft while remaining close enough to intercept any Japanese naval forces advancing beyond the Louisiades through either the Jomard Passage or the China Strait. Low on fuel and not in contact with Fletcher, who was maintaining radio silence and had not informed him in advance, Crace had no idea of Fletcher's location, status, or intentions.

Zuikaku monitored a message from a Deboyne-based reconnaissance aircraft incorrectly reporting that Crace's force had altered course to 120° true (southeast). Takagi's staff assumed the aircraft was shadowing Fletcher's carriers and determined if the Allied ships held that course, they would be within striking range shortly before nightfall. Takagi and Hara begin preparing to attack immediately with a select group of aircraft, minus fighter escort, even though it meant the strike would return after dark.

Hoping to confirm the location of the Allied carriers, Hara ordered the flight of eight torpedo bombers as scouts to sweep 200 nmi (230 mi; 370 km) westward. About that same time, the dive bombers returned and landed from their attack on the Allied ships earlier. Six of the weary dive bomber pilots were told they would be immediately departing on another mission. Choosing his most experienced crews, Hara launched twelve dive bombers a fifteen torpedo planes with orders to fly bearing 277° to 280 nmi (320 mi; 520 km). The eight scout aircraft reached the end of their 200 nmi (230 mi; 370 km) search leg and turned back without seeing Fletcher's ships.

Operating under thick overcast 200 nmi (230 mi; 370 km) west of Takagi, TF 17 detected the Japanese strike on radar heading in their direction, and turned southeast into the wind, vectoring eleven CAP Wildcats to intercept. Taking the Japanese formation by surprise, the Wildcats shot down seven torpedo bombers and one dive bomber, and heavily damaged another torpedo bomber which later crashed, at a cost of three Wildcats lost. With their formations scattered and suffering heavy loses in the attack, the Japanese strike leaders canceled the mission after conferring by radio. The Japanese aircraft all jettisoned their ordnance and reversed course to return to their carriers.

About thirty minutes after sunset, several of the Japanese dive bombers encountered the Allied carriers in the darkness, and briefly confused as to their identity, circled in preparation for landing before anti-aircraft fire from TF 17's destroyers drove them away. An hour later TF 17 and Takagi were about 100 nmi (120 mi; 190 km) apart. Takagi turned on his warships' searchlights to help guide the eighteen surviving aircraft back and all were recovered by that night.

In the meantime one of the Allied ships that was struck earlier in the day was able to radio TF 17 to inform the Allied command that she was drifting northwest in a sinking condition. The ship's report gave wrong coordinates, which would hamper subsequent Allied rescue efforts to locate the doomed oiler. More significantly, the news informed Fletcher his only nearby available fuel supply was gone.

As nightfall ended aircraft operations for the day, Fletcher ordered TF 17 to head west and prepared to launch a 360° search at first light. Crace also turned west to stay within striking range of the Louisiades. Inoue directed Takagi to make sure he destroyed the Allied carriers the next day, and postponed the Port Moresby landings to 12 May. Takagi elected to take his carriers 120 nmi (140 mi; 220 km) north during the night so he could concentrate his morning search to the west and south and ensure that his carriers could provide better protection for the invasion convoy. Late that night Gotō and Kajioka were unable to position and coordinate their ships in time to attempt a night attack on the Allied warships. Both the Japanese and the Allied ships expected to find each other early the next day, and spent the night preparing their strike aircraft for the anticipated battle as their exhausted aircrews attempted to get a few hours sleep.

Aleutian Islands Campaign
While the main focus of the Japanese offensive against the American Pacific-Asiatic Zone was centered around the shipping route between Hawaii and the Philippines, and its fleet at Pearl Harbor, the Japanese navy also gathered information about the Aleutian Islands of the Republic of Alaska, an important chain of outlying islands off Alaska Proper. Updated reconnaissance and intelligence reports regarding military development and ship movements created a detailed picture of the strategic situation on the Aleutian Islands. Admiral Isoroku Yamamoto provided the Japanese Northern Area Fleet, commanded by Vice-Admiral Boshiro Hosogaya, with a force of two small aircraft carriers, five cruisers, twelve destroyers, six submarines, and four troop transports, along with supporting auxiliary ships. With that force, Hosogaya was ordered to launch an air attack against Dutch Harbor, followed by an amphibious attack upon the island of Adak, 480 miles to the west. Hosogaya was instructed to destroy whatever American forces and facilities he located on Adak to cripple the nation of Alaska. What the Japanese did not realize was how lightly defended the Alaskan mainland was.

Following Hosogaya's successful completion of his mission, his men were to return to their ships and act as a reserve force for two additional landings in the Aleutian Islands. The first additional landing was to be at Kiska, 240 miles west of Adak, followed by a second landing on the Aleutians' westernmost island, Attu, 180 miles west from Kiska.