When Seaman "Happy" Hanes meets some Marines, he greets them by saying "Which one of you is John Wayne?" This movie is set in 1943. However, John Wayne didn't portray a Marine until 1949 in "The Sands of Iwo Jima".
During the opening credits, a helicopter fly-by shot zooms in on the PT-73, showing McHale and a seaman (in blue shirt and white sailor hat) at the helm. In the next shot, as the PT-73 pulls up to an island dock, McHale and Ensign Parker are at the helm.
McHale, and all officers in the film (Ensign Parker, Captain Binghampton, and Lieutenant Carpenter) wear brown low-quarter uniform dress shoes. This is incorrect, as traditionally, only naval aviators (flyers) wear brown shoes. The U.S. Navy has always differentiated between the "black-shoe" (ship and submarine officers and men) and the "brown-shoe" (naval flying officers and men) Navy(s).