At the end of World War One, America's foreign policy could be summed up in two words: Never again. Many Americans felt the Great War was a great mistake, and hoped that it was indeed "the war to end all wars." And if war was obsolete, then a strong military force was unnecessary.
Between 1918 and 1940, the U.S. armed forces were too few men, inadequately armed. The Army hadn't had a pay raise since 1920. Most soldiers were hard-drinking, hard-bitten, semi-literate old lifers. (Think Ernest Borgnine in From Here to Eternity.) Promotion took years, for buck privates up to generals, who usually had two years of service left before they reached mandatory retirement. The four top Army field commanders throughout WW2 first saw action in the Spanish-American War.
The Navy was the same, filled with men who preferred being sailors to being unemployed. Re-enlistment was near 90%, so only one out of every 18 recruits was accepted. The Navy was especially affected by military spending cuts during the Depression. Older battleships' crews were reduced by as much as 60%; the Marines' manpower went down 25%.
Even more problematic was the equipment fighting men were given. In 1936, the Army General Staff reported that in the event of deployment, troops "can be supplied with required equipment from storage, except for airplanes, tanks, combat cars, anti-aircraft guns, and 50 caliber machine guns." Five years later, the average infantryman was still armed with a 1903 Springfield rifle. And the regulation artillery piece had been declared inadequate…in 1918. Yet the 1939 military budget allocation for research and development was less than 2%, or 1/400th what the A bomb would cost to develop.
There was some hope. Boeing produced the first B17 bomber in 1935, eventually fitted with Dutch immigrant Carl Norden's indispensable bombsight. The Navy had the best submarines in the world, even if they were armed with the worst torpedoes. And the new President, a former under secretary of the Navy named Roosevelt, was far more interested in supporting the military than his predecessor.
Finally, because of the Depression, America was filled with idle factories and idle workers—men and women of great skill who were just waiting to go back to work. They were ready for a challenge, and would meet it spectacularly.