The first thing after war begains, would be the taking of 111 world war destroyers out of mothballs. Then 10 large, slow passenger liners would be converted into XCVs. Each one capable of operating 60 aircraft. Congress would have passed an 80% fleet expansion bill for naval construction in 1939. 6 fast battleships of the South Dakota class, and 5 fleet carriers of the Yorktown class would have been laid down during 1939 and early 1940. Also 10 cruisers of the Witchita and Brookln classes would have been begun. Plus 58 Benson class DDs.
The army intended to mobilize 750,000 army troops and 50,000 marines to fight a pacific war. Another one and a half million soldiers would have been drafted to form a strategic researve in the United States.
The army would have required 2 full years to train and equip this new large army. Plus time to design and build landing craft. No offensive moves into the Western Pacific could have been conducted sooner than 2 years.
Also the conversion of the XCVs would have required 2 years. 18 months to convert them and 6 months to train their air groups. The 58 Benson class DDs laid down in 1939 would have been available in time for offensive action in early 1941. But the Carriers and cruisers wouldn't have been ready until mid 1942. If we assume that war broke out in January of 1938, Offensive action would have been delayed until 3 years after the outbreak of war.
Huge numbers of transports and tankers would have to be built. So the fleet might have embarked of an invasion of Truk by December of 1940.
But here's the rub. The U S might have gotten involved in a European war long before a cross pacific offensive could have begun. This might not have been such a bad thing however. Perhaps the U S would have sent 9 divisions to France in response to a war breaking out over Czecheslovokia.
Initially, Britain, France and the Soviet Union were allied against Germany. With both Yugoslavia and Romainia warning Hungury they would declair war on her if she joined Germany against the czechs. Italy was scared spitless and vowed to remain strictly neutral.
If the U S joined this coaliton to face down Hitler. The European war might have only lasted a year. Or might have not happened at all.
An early U S build up in 1938 could have paid big dividends.
And after the dust settled in Europe, this same coalition might have been able to force Japan to negotiate and end to the Pacific war. Japan wouldn't have tried to fight the U S, britain, France and the Soviet Union simultaneously. They were fanatic, but not stupid.
In another possibility. In 1939, war breaks out in Europe with the invasion of Poland. The U S ends up sending the army and air corp to France. 15 divisions and 15 air groups prevent the Germanys from defeating France. Over the next 2 years, another 30 divisions and 40 air groups arrive to hold off the Germans. Would the Soviet Union have honored their non agression pact with the nazies?
If the U S stayed out of the European war. Then by the end of 1942 they would have been in position to advance into the Phillipines.
A fleet expansion would have seen 6 new fast battleships and 6 fleet carriers being laid down in 1940, These carriers would have been available in early 1943.Teamed up with 6 fast battleships of the south dakota class laid down in 1939, The navy would have been able to recapture the Phillipines and sever the oil from the south. One wonders if an invasion of Japan would have been contimpated in this scenario? Possibly a multi year blockaide as was originally planed would have been set up.
If there was no U S intervention in Europe, would the British, French and Soviets been able to defeat Hitler. I would say their chances were pretty good.
And a U S defeat of Japan might have been accomplished only by stratiegic bombing and a blockade.