They Were Expendable is a 1945 American war film directed by John Ford, starring Robert Montgomery and John Wayne, and featuring Donna Reed. The film is based on the 1942 novel of the same name by William Lindsay White, relating the story of the exploits of Motor Torpedo Boat Squadron Three, a United States PT boat unit defending the Philippines against Japanese invasion during the Battle of the Philippines (1941–42) in World War II.

While a work of fiction, the book was based on actual events and people. The characters John Brickley (Montgomery) and Rusty Ryan (Wayne) are fictionalizations of PT-Boat Squadron Three Commander John D. Bulkeley, a Medal of Honor recipient, and his executive officer Robert Kelly, respectively. Both the film and the book, which was a best-seller and excerpted in Reader's Digest and Life, depict certain combat-related events that were believed to have occurred during the war, alongside those which did not; nonetheless, the film is noted for its relatively accurate and detailed depiction of naval combat for the era in which it was made.