The movie takes place in World War II - before the Pearl Harbor attack. After attempting to join the U.S. Navy, Henry (a shy bookkeeper with a passion for fish) is rejected, due to his poor eyesight. Thoroughly downtrodden, he takes a walk along the Coney Island pier and accidentally falls into the water - turning into a talking fish. As the story unfolds, Limpet is commissioned by the Navy (complete with advancing rank and salary) to defeat the Nazis in The Battle of the Atlantic - finding Nazi U-boats and disrupting their underwater measurements and weapons with an intense "thrum" noise he is able to emit, now that he is a fish. He falls in love with "Lady Fish" (the complete opposite of his overbearing, human wife Bessie... who now presumes he is dead); being a good guy, Henry continues to send money home to his old biddy of a wife. I'm sure that by today's standards, Henry Limpet would be considered a loser, and the film a total flop, but I loved everything about this movie as a child; I loved that Henry's passion for fish turned into his reality, that "reality" was in cartoon form, and that the meek one became the hero.
* this is an 18"x24" piece I recently painted of "The Incredible Mr. Limpet"