[Chad C. Mulligan]

The first US ship lost in WWII wasn’t from the Japanese, it was torpedoed by a Uboat as it did convoy escort. (USS Reuben James)

The first ship lost to enemy action by a WW2 opponent was the USS Panay, sunk by the Japanese in 1937.

From the U.S. Naval Institute account of the incident:

"The isolationist mood of the United States precluded any strong and decisive action following the Panay incident. Roosevelt’s Quarantine Speech in Chicago in October of 1937 resulted in a negative reaction from the isolationists who wished a strong implementation of the Neutrality Acts of 1937; and after the Panay incident, wanted a complete withdrawal of our naval forces, Marines, businessmen, and missionaries from the Far East."

Nothing positive was done, and on December 7, 1941. . . . .

[DesertRhino]

That’s April 1941 when they started. That was the mercenary phase. At two weeks after Pearl Harbor is when they were made part of the US Air Force. That’s also when pappy Boyington left and came back home to rejoin the Marines.

[Pete Dovgan]

What year did WWII start?

I don’t believe 1937 is the recognized year.