The Elco boats were the largest in size of the three types of PT boats built for U.S. use during World War II. Wooden-hulled, 80 feet long with a 20-foot, 8-inch beam, the Elco PT boats had three 12-cylinder Packard gasoline engines generating a total of 4,500 horsepower for a designed speed of 41 knots. With accommodations for 3 officers and 14 men, the crew varied from 12 to 14. Its full-load displacement was 56 tons. Early Elco boats had two 20mm guns, four .50-caliber machine guns, and two or four 21-inch torpedo tubes. Some of them carried depth charges or mine racks. Later boats mounted one 40mm gun and four torpedo launching racks. Many boats received ad-hoc refits at advanced bases, mounting such light guns as Army Air Forces 37mm aircraft guns and even Japanese 23mm guns. Some PTs later received rocket launchers.

Originally conceived as antiship weapons, PTs were publicly, but erroneously, credited with sinking Japanese warships during the early months after Pearl Harbor. During the long Solomons campaign, they operated usefully at night and times of low visibility against Japanese barge traffic in the "Slot." Throughout World War II, PTs operated in the southern, western, and northern Pacific, as well as in the Mediterranean and the English Channel. Some served off Normandy during that invasion. Though their primary mission continued to be seen as attack of surface ships and craft, PTs were also used effectively to lay mines and smoke screens, to rescue downed aviators, and to carry out intelligence or raider operations. Almost all surviving Elco PTs were disposed of shortly after V-J Day. One Elco boat, PT 617, survives at Battleship Cove, Fall River, Massachusetts.

Although more 80-foot Elco boats were built than any other type of motor torpedo boat, other types were built by the U. S. The British-designed 70-foot Vosper boats which were built for Lend Lease fired 18-inch torpedoes. Since the U.S. produced the heavier and longer 21-inch torpedoes, the U.S. Navy wanted a larger PT boat. After experimentation, the first PT boat built in any quantity was the 77-foot type built by Elco. These boats were used early in World War II. In 1943 in the Solomons, three of these 77-foot PT boats, PT 59, PT 60 and PT 61, were even converted into gunboats by stripping the boat of all original armament except for the two twin .50 caliber gun mounts, and then adding two 40mm guns and four more twin .50 caliber machine guns. LTJG John F. Kennedy was the first commanding officer of PT 59 after the conversion.