Plot summary

The story begins before the U.S. becomes involved in World War II, before the attack on Pearl Harbor. Shy bookkeeper Henry Limpet loves fish with a passion. Rejected by the U.S. Navy and feeling downcast, he falls off a pier into the waters near Coney Island and finds he has turned into a fish. Since he never resurfaces, his wife and friends assume he has drowned.

The animated fish Limpet, complete with his signature spectacles, discovers a new-found ability during some of his initial misadventures, his “whale-busting” thrum. During this time he falls in love with a female fish named “Ladyfish”, and rejects his overbearing human wife, Bessie, in the process.

Still determined to help the Navy, Limpet finds the ship on which one of his friends, George Stickel, is stationed. Ultimately, Limpet is commissioned by the U.S. Navy, complete with advancing ranks and salary, which he has sent to Bessie, to assist in the hunt for Nazi U-boats. He plays a large part in the Allied victory in the Battle of the Atlantic.

The choice of the name “Limpet” for the main character is somewhat ironic: While limpets are aquatic, in their adult form they are nearly immobile mollusks that cling to rocky shorelines. The name was probably chosen as a reference to the Limpet mine, a type of naval mine used during WWII, since Henry essentially used his “thrum” as a weapon.