The US Navy's experience with Motor Torpedo Boats (aka PT Boats) started in the 1930s after examining the effectiveness of the Fast Torpedo Boats developed and employed by the British, French and Italian navies during World War I. The first eight PT Boats developed for the US Navy were less than impressive.
The Electric Boat Company (ELCO) acquired a British torpedo boat which impressed the Navy enough to put ELCO under contract to develop PT Boats based upon the British design but featuring a number of changes, including power from three navalized Packard Liberty V-12 aircraft engines rated initially at 1100 horsepower, but reaching 1500 horsepower each by war's end.
Initially deployed as a torpedo boat, early PTs were armed with torpedo launch tubes that were powered by compressed air. These were later replaced with simple racks that were powered by gravity. As the war progressed, the PT Boat's mission changed to an interdiction role where Japanese supply boats and barges were sunk. As this role became more successful, PT Boats were reconfigured from torpedo launch platforms to gun boats, some of which also carried rocket launchers.
The Elco 80' boats were the most numerous in US Navy service with 326 examples built. These were numbered in groups: 103-196, 314-367, 372-383, 486-563, 565-622.