World War II Secret Baseball Passwords
Exciting Sports, A Thrilling Publication, 1944.
In WWII, German soldiers that spoke good English would infiltrate Allied territory as spies and saboteurs. They wore stolen American uniforms or they posed as simple country folk with forged identification cards.
If someone was suspected as a German spy, they would be asked questions about baseball. Inevitably they would give themselves away, after all, they could not possibly be Americans if they couldn't answer some baseball trivia.
Sometimes this worked and they captured German spies and other times it did not work out so well.
In the Pacific theater, military brass approved resources for field construction and sent out teams stocked with Major Leaguers to play exhibition games for the troops as a morale booster.