Was it over when the Germans bombed Pearl Harbor?
Funny reply.
As you well know, Pearl Harbor was bombed in the last days of 1941...
Hitler actually began his mischief in 1938 with the Anschluss and invasion of the Sudetenland and things got really hot in 1939 with the ultimatum and hotter in September of 1939 with the invasion of Poland.
"Lend-Lease" began in 1940, mostly to our European allies - most of whom needed weapons to fight Hitler & company. This pulled the USA out of the depression - the actions of the madman, Adolf Hitler, and not the actions of the Socialist economic illiterate FDR.
US Military production kicked into full steam a full 2 1/4 years before Pearl Harbor - which was a 'surprise attack'.
Funny answer though.