How strong was the U.S. military in WWII? 

During World War II, the U.S. military was the strongest existence on the surface of the earth.
Look at World War II, look at the Soviet Union for the land battle, and look at the United States and Japan for the naval battle. After Japan attacked Pearl Harbor, the Pacific War dominated by the United States and Japan broke out.
In several major naval battles, such as the Battle of the Coral Sea and the Battle of Midway Island, a large number of aircraft carriers from both sides participated in the battle, and the carrier-based aircraft launched an air battle.