PT boats were a variety of torpedo-armed fast attack craft used by the United States Navy in World War II to attack larger surface ships. "PT" is the US hull classification symbol for "Patrol Torpedo". The PT boat squadrons were nicknamed "the mosquito fleet". The Japanese called them "devil boats".
The original pre–World War I torpedo boats were designed with "displacement" hulls. They displaced up to 300 tons and the top speed was 25 to 27 kn (29 to 31 mph; 46 to 50 km/h). The PT boats used in World War II were built using the planing-type hull form developed for racing boats. They were much smaller (30–75 tons) and faster (35 to 40 kn (40 to 46 mph; 65 to 74 km/h)). Both types were designed to strike at larger warships with torpedoes, using relatively high speed to get close, and small size to avoid being spotted and hit by gunfire. They were much less expensive than large warships. PT boats were much faster, smaller, and cheaper than conventional (displacement hull) vessels.
During World War II, American PT boats engaged enemy destroyers and numerous other surface craft, ranging from small boats to large supply ships. PT boats also operated as gunboats against enemy small craft, such as armored barges used by the Japanese forces for inter-island transport.
The primary anti-ship armament was two to four Mark 8 torpedoes, which each weighed 2,600 pounds (1,179 kg) and contained a 466-pound (211 kg) TNT warhead. These torpedoes were launched by Mark 18 21-inch (530 mm) steel torpedo tubes. Mark 8 torpedoes had a range of 16,000 yards (14,630 m) at 36 knots (41 mph). Common to all US PT boats were two twin M2 .50 cal (12.7 mm) machine guns. Another automatic weapon commonly mounted on PT boats was the Oerlikon 20 mm cannon. All U.S. PT boats were powered by three 12-cylinder gasoline-fueled engines running on high octane aviation gasoline (AvGas). These engines were built by the Packard Motor Car Company, and were a modified design of the 3A-2500 V-12 liquid-cooled aircraft engine.
As early as 1922, the US Navy considered using small internal combustion engine powered torpedo boats. As a result, two types of WW1 vintage British Royal Navy Coastal Motor Boats were obtained for testing. After failing the testing period, the small boats were rejected from further consideration. Then 17 years later, in 1939, the U.S. Navy renewed their investigation into the concept by requesting competitive bids for several different types of motor torpedo boats. This competition led to eight prototype boats built to compete in two different classes. The first class was for 55-foot (17 m) boats, and the second class was for 70-foot (21 m) boats. The resulting PT boat designs were the product of a small cadre of respected naval architects and the Navy.
On 8 June 1939, contracts were let to the Fogal Boat Yard, Inc., later known as the Miami Shipbuilding Co., of Miami, Florida, for PT-1 and -2 "Crash Boats", and to the Fisher Boat Works, Detroit, Michigan, for PT-3 and -4. These four boats were essentially the Crouch design, modified in some details by the Bureau of Ships.
Then were the three boats built by Andrew Jackson Higgins of Higgins Industries in New Orleans. These boats were PT-5 and PT-6 (built using government-required Sparkman and Stephens design, scaled to an overall length of 81 feet (25 m)) and then PT-6 "Prime" which was redesigned by Andrew Higgins personally using his own methods. Later that same year, Higgins was to build PT-70 that incorporated slight improvements over PT-6 Prime.
The Philadelphia Navy Yard simultaneously began construction of two other boats (PT-7 and PT-8), created by designers at the Navy Yard and the Navy Bureau of Ships. These boats were constucted mainly out of aluminum and had 4 engines.
Henry R. Sutphen of Electric Launch Company (Elco) and his designers (Irwin Chase, Bill Fleming, and Glenville Tremaine) visited the United Kingdom to see British motor torpedo boat designs. While visiting the British Power Boat Company, they purchased a 70-foot (21 m) design (PV70) (later renamed PT-9 during the competition), designed by Hubert Scott-Paine. This boat PT-9 was to serve as the prototype for all future Elco designed PT Boats.
The final competitor for the contract was Huckins Yacht Corporation of Jacksonville, Florida, which came up with competing 70-foot (21 m) boat class designs. PT-69
The competition monetary prizes for each of the designs were paid to all of these competitors by the US government. However, rigorous testing performed on each design revealed problems that had to be fixed before they could meet required performance specifications. As a result, the Navy, ordered further investigation and refinement of the existing designs until a satisfactory working design could be obtained.
The Plywood Derby
The Board of Inspection and Survey decided to conduct comparative service tests. The following boats were tested off New London, 21 to 24 July 1941:
- PT-6: 81 ft (25 m) Higgins; 3 Packard 1,200-hp engines.
- PT-8: 81 ft (25 m) Philadelphia Navy Yard; aluminum hull; 2 Allison 2,000-hp engines, 1 Hall-Scott 550-hp engine.
- PT-20: 77 ft (23 m) Elco; 3 Packard 1,200-hp engines; equipped with special propellers; special strengthening added to hull framing and deck.
- PT-26, -30, -31, -33: Same as PT-20, except with standard propellers and without special strengthening.
- PT-69: 72 ft (22 m) Huckins; 4 Packard 1,200-hp engines.
- PT-70: 76 ft (23 m) Higgins; 3 Packard 1,200-hp engines.
- One 70 ft (21 m) MRB (Motor Rescue Boat) boat built for the Dutch Navy by Higgins; 3 Hall-Scott 900-hp engines.
The test included an open-sea run of 190 miles (310 km) at full throttle, forever after referred to by PT personnel as the "Plywood Derby." The course started around New York Harbor, at Sarah Ledge, then led around the eastern end of Block Island, then around Fire Island Lightship, finishing at Montauk Point Whistling Buoy.
This was a shakedown to see which company would be contracted to build the Navy PT boats. At the completion of the trials, the Navy considered all three designs as successful. The Elco 77-footer (23 m) (PT-20) came in first with an average speed of 39.72 kn (45.71 mph), followed by the Huckins 72-foot (22 m) boat (PT-69) and the Higgins 76-footer (23 m) (PT-70). The Navy saw the merits of the other two boats and decided to offer all three companies contracts. Elco received the largest share of the contract with contracts for 350 boats, Higgins was awarded contracts for 199 boats, and Huckins was awarded a contract for 18 boats.
The Elco Company may have had an advantage owing to their experience in small-boat building, having built 550 80 ft (24 m) sub chasers for the Royal Navy during World War I. Additionally, in 1921, they introduced the famous 26 ft (7.9 m) "Cruisette", (a gasoline cabin cruiser). This success in small-boat building was followed in the 1930s with 30-ft to 57-ft "Veedettes" and "Flattops", which were gasoline-powered boats that set the highest standard in a golden era of boating. This small-boat experience helped Elco obtain a contract for 10 boats based on the 70-foot (21 m) Scott-Paine Model PT boat. These 70 ft (21 m) boats were tested and determined to be too light for open sea work, but Elco got a contract for 24 larger boats based on a lengthened 77 ft (23 m) design. This Elco 77 ft (23 m) design was considered acceptable for future construction provided changes were made to reduce pounding in a seaway, and also strengthen the structure in a manner acceptable to the Bureau of Ships.
ELCO and Higgins PT boats, as published in a 1945 training manual
The Elco Naval Division boats were the largest in size of the three types of PT boats built for the Navy used during World War II. By war's end, more of the Elco 80 ft (24 m) boats were built than any other type of motor torpedo boat (326 of their 80 ft (24 m) boats were built). The 80 ft (24 m) wooden-hulled craft were classified as boats in comparison with much larger steel-hulled destroyers, but were comparable in size to many wooden sailing ships in history. They had a 20 ft 8 in (6.30 m) beam. Though often said to be made of plywood, they were actually made of two diagonal layered 1 in (25 mm) thick mahogany planks, with a glue-impregnated layer of canvas in between. Holding all this together were thousands of bronze screws and copper rivets. This type of construction made it possible for damage to the wooden hulls of these boats to be easily repaired at the front lines by base force personnel. Five Elco Boats were manufactured in knock-down kit form and sent to Long Beach Boatworks for assembly on the West Coast as part of an experiment and as a proof of concept.