Lt. Rip Crandall (Jack Lemmon) is entrusted with one of the most important missions of his World War II career: to shuttle an Australian spy (Chips Rafferty) into enemy territory. Unfortunately, he'll be doing it with one of the Navy's least seaworthy vessels, the USS Echo. But even in a clunker of a ship, Crandall and his madcap crew -- including his enthusiastic young ensign (Ricky Nelson) -- do their best to make their ill-equipped mission a success.