A nickname sailors gave for the quad 1.1"/75 caliber anti-aircraft gun used during World War II. The gun was commonly found on navy ships.
The Japanese fighter made it past the ship's fighter screen, but it was shot down by a Chicago Piano.
1920's big-city term when mobsters refered to their tommy guns as "pianos" Al Capones and Bugs Morans gangs went to the mattresses with their chicago pianos.
old lady: what do you gentlemen have in those cases, violins?
mobster: no ma'am their our pianos, and we get paid well for playing them