The Pt Boat's Engine: Powering America's Wwii Naval Legacy

PT boats, or Patrol Torpedo boats, were used by the United States Navy during World War II. They were small, fast, and inexpensive to build, and were valued for their speed and manoeuvrability. All PT boats were powered by three 12-cylinder gasoline-fuelled engines built by the Packard Motor Car Company. The engines were modified versions of the 3A-2500 V-12 liquid-cooled aircraft engine, and were designated as 3M-2500, 4M-2500, and 5M-2500, with each new iteration offering slight improvements over the last.

PT boat engines were modified from the Packard 3A-2500 aircraft engine

PT boats, or Patrol Torpedo boats, were used by the US Navy in World War II. They were small, fast, and inexpensive to build, and were valued for their speed and manoeuvrability.

The 3M-2500 was an experimental engine that Packard lost $300,000 on in 1939. However, the challenges were overcome, and the engine was redesigned with an aluminium block, steel cylinder sleeves, and a centrifugal supercharger; later models were also fitted with an intercooler. The 4M-2500 was an updated Packard Liberty engine introduced in 1924. The 5M-2500, introduced in late 1945, had a larger supercharger, aftercooler, and increased power output of 1,850 hp.

The engines were four-stroke, water-cooled, 60-degree V-type engines with a 6-3/8" bore and 6-1/2" stroke, for a total of 2490 cubic inches of displacement. Each engine had 48 valves, 2 inlet and 2 outlet per cylinder, and a compression ratio of 6.4:1. They were fitted with a gear-driven centrifugal supercharger and intercooler, and used aircraft-type dual magneto sparks and two spark plugs per cylinder. The engines developed 1850 hp at 2500 rpm, with a max revolution of 3000 rpm. The engine weight was 3100 pounds. These engines were designed to burn 100 octane aviation gasoline to achieve nominal power output.

PT boats were powered by three 12-cylinder gasoline-fuelled engines

PT boats, or Patrol Torpedo boats, were used by the US Navy in World War II. They were small, fast, and inexpensive to build, and were valued for their speed and manoeuvrability.

The three successive versions of these engines were designated as 3M-2500, 4M-2500, and 5M-2500, each of which had slight improvements over the previous version. Their aircraft roots gave them many features of aircraft engines, such as superchargers, intercoolers, dual magnetos, and two spark plugs per cylinder. Packard built the Rolls-Royce Merlin aero engine under license alongside the 4M-2500, but with the exception of the PT-9 prototype boat, the Merlin was never used in PTs.

The 4M-2500s initially generated 1,200 hp (895 kW) each, together roughly the same power as a Boeing B-17 bomber. They were subsequently upgraded in stages to 1,500 hp (1,150 kW) each, for a designed speed of 41 knots (76 km/h). The final engine version, the Packard 5M-2500, (late 1945) had a larger supercharger, aftercooler, and power output of 1,850 hp. This much power could push the fully loaded boats at 45 to 50 knots. However, using the older 4M-2500 engines, increases in the weight of the boats due to more weaponry offset the potential increase in top speed.

Fuel consumption of these engines was phenomenal; a PT boat carried 3,000 gallons (11,360 liters) of 100 octane avgas. A normal patrol for these boats would last a maximum of 12 hours. The consumption rate for each engine at a cruising speed of 23 knots was about 66 gallons (250 l) per hour (200 gallons [760 l] per hour for all 3 engines). However, at top speed, consumption increased to 166 gallons (628 l) per hour per engine (or 500 gallons [1,890 l] per hour for all 3 engines). Navy acceptance trials for every boat required it be able to demonstrate the ability to achieve a design speed of 41+ knots. Going at this speed, the 3,000 gallons of fuel would be used in only about 6 hours. Wartime conditions such as hull fouling and engine wear could sometimes cause the boats' top speed to be degraded until maintenance could be performed.

PT boats were designed to strike larger warships with torpedoes

PT boats, or Patrol Torpedo boats, were a type of motor torpedo boat used by the United States Navy during World War II. They were small, fast, and inexpensive to build, and were valued for their speed and manoeuvrability. They were designed to strike larger warships with torpedoes, and their primary anti-ship armament was four 21-inch Mark 8 torpedoes, each with a 466-pound TNT warhead and a range of 16,000 yards at 36 knots.

PT boats were very different from the first generation of torpedo boats, which had been developed in the 19th century and rode low in the water. PT boats were designed to exploit advances in planing hull design borrowed from offshore powerboat racing, and used multiple lightweight but powerful marinized aircraft-derived V-12 engines. This allowed them to advance in both size and speed.

PT boats were organised into Motor Torpedo Boat Squadrons (MTBRONs) and were nicknamed "the mosquito fleet" and "devil boats" by the Japanese. They were designed to be fast and agile enough to counter the threat of battleships and other slow and heavily-armed ships. They were also expendable, and a swarm of PT boats attacking en masse could overwhelm a larger ship's ability to fight them off.

PT boats were first conceived as anti-ship weapons and were credited with sinking several Japanese warships during the early months after Pearl Harbor. However, their torpedoes were ineffective at the beginning of the war, and PT boat crews attacking at night may have failed to note torpedo failures. PT boats were also vulnerable to attack by Japanese seaplanes, which could easily spot the phosphorescent wake left by their propellers.

PT boats were eventually fitted with Raytheon SO radar, which gave them a distinct advantage in intercepting enemy supply barges and ships at night. They were also used to lay mines and smoke screens, rescue downed aviators, and carry out intelligence or raider operations.

PT boats were powered by three marine-modified derivations of the Packard 3A-2500 V-12 liquid-cooled, gasoline-fuelled aircraft engine. The Packard 4M-2500 and 5M-2500 supercharged engines generated between 1,200 and 1,850 hp, allowing a designed speed of 41 knots.

PT boats were faster, smaller and cheaper than conventional vessels

PT boats, or Patrol Torpedo boats, were used by the US Navy in World War II. They were faster, smaller and cheaper than conventional vessels, and were valued for their speed and manoeuvrability.

PT boats were much smaller than conventional vessels, weighing between 30 and 75 tons, compared to the 300 tons of the first generation of torpedo boats. They were also faster, with a top speed of 40 knots, compared to the 25-27 knots of the first generation.

PT boats were also much cheaper than conventional vessels. They were inexpensive to build, and their wooden hulls were easy to repair. This meant that PT boats could be produced quickly and in large numbers.

PT boats were powered by three 12-cylinder gasoline-fuelled engines, which were a modified version of the 3A-2500 V-12 liquid-cooled aircraft engine. These engines were built by the Packard Motor Car Company, and generated a total of 4,500 horsepower.

PT boats were typically armed with two to four Mark 8 torpedoes, each weighing 2,600 pounds and containing a 466-pound TNT warhead. They also carried two twin M2 .50 calibre machine guns, and some were equipped with a 20mm Oerlikon cannon.

PT boats played an important role in World War II, particularly in the Pacific. They were used to attack enemy destroyers, barges, and other surface craft. They were also used as gunboats, and for laying mines and smoke screens, rescuing shipwreck survivors, and carrying out intelligence operations.

PT boats were used as barge busters

PT boats were used as "barge busters" to disrupt enemy supply lines. The Allies had air superiority during the day, so the Japanese and Germans shifted their supply missions to night-time, using shallow-draft barges in shallow waters. PT boats were perfect for this role, as destroyers were unable to follow them into shallow waters. The PT boats were able to sink the barges, despite their torpedoes being ineffective against the shallow-draft barges. To accomplish this task, PT boats were retrofitted with more and heavier guns.

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