A PT boat (short for Patrol Torpedo boat) was a torpedo-armed fast attack craft used by the United States Navy in World War II. It was small, fast, and inexpensive to build, valued for its maneuverability and speed but hampered at the beginning of the war by ineffective torpedoes, limited armament, and comparatively fragile construction that limited some of the variants to coastal waters. Propulsion was via a trio of Packard 4M-2500 and later 5M-2500 supercharged gasoline-fueled, liquid-cooled marine engines.