Authored By Dan Alex (Updated: 8/2/2016):
In the late 1930s, the world was on the verge of war once again as national armies ramped up development and production amidst a Great Depression. Germany and Italy became active within Europe (with a little bloody help from the Spanish Civil War) while the Japanese Empire moved into China. The US military initially developed three designs to fulfill their PT boat need (further divided into a 55-foot and 70-foot class) and a total of eight vessels - numbered "PT-1" through "PT-8" - were ultimately produced. While serviceable naval vessels in their own right, the group lacked the performance and capabilities that the USN sought.
After a visit to Europe, ELCO representatives procured a high speed boat from British Power Boat Company. The boat was based on a Hubert Scott-Paine design and initially designed as a private venture around an advanced speed boat measuring 70 feet from bow to stern. ELCO utilized this design as the basis for its 40-ton PT submission (also known as the "Scott-Paine Boat") and armed the type to USN specifications with 4 x 457mm British-length torpedo launchers. The USN assigned the boat the designation of "PT-9" and formally accepted the type on an experimental basis, ordering 10 examples as PT-10 through PT-19 and requiring use of 3 x Packard marine gasoline engines of 1,200 horsepower each as well as revised crew areas. These vessels entered USN service in November of 1940.
However, the USN was not fully satisfied with these 70-foot PT boats for they lacked the necessary space to mount the 533mm torpedo. Additionally, the 70-foot hull length of the PT-9 class shown itself to suffer in unforgiving open sea environments. As such, the USN came to ELCO once more - this time with a refined set of changes to their 70-foot design - and contracted for 24 new vessels to be designated PT-20 through PT-44. Most important of these revisions was the increasing of the 70-foot the hull length to 77 feet to help compensate for both rough seas handling and the longer USN 533mm torpedo.
By this time, and before American involvement in World War 2, the Board of Inspection and Survey (of the US Navy Department) took to a new competitive trial to take place offshore of New London during a mid-summer's week in July of 1941. In the testing, new boat designs were submitted from ELCO, Higgins and Huckins. While the USN maintained experience in working with ELCO from earlier, Higgins and Huckins both took to designing competing PT boat systems as private ventures. The final group of seven boats (including the ELCO PT-20) entered into the competition measured between 70 and 81 feet in length and were trialed through various exercises including operations out at sea. This event came to be known historically as the "Plywood Derby" and would decide the true winner of the lucrative USN PT boat contract (the "plywood" name despite the fact that the boats were not constructed of plywood at all).
All that said, USN representatives actually found the submissions from the three major manufacturers worthy of further development. When notes were officially tallied, the ELCO design was the frontrunner because of its inherent handling and speed though it suffered in rough seas. The Higgins 76-footer and the Huckens 72-footer were both admirable endeavors in their own right and, as a result, the USN offered all three concerns individual contracts for development and production of their respective PT boat designs. Of the three, however, ELCO would remain the largest producer of PT boats for the American Navy for the duration of the upcoming war. The design was also furthered by the USN request for a longer 80-foot hull by ELCO based on their 77-foot design - this becoming the famous "PT-103" class of torpedo boats used in large numbers throughout the upcoming war.
All USN PT boats were powered by 3 x Packard 2500 series V-12, centrifugal gear-driven, 100 octane gasoline-fueled, water-cooled engines exhausting through six ports at the outboard stern wall. These powerplants were based on an existing - though modified for marine service - aircraft engine, the Packard 3A-2500 (this engine itself originating back to the American "Liberty" bomber engine of 1925). By this time, ELCO had modified the engine to serve in marine vessels and used an "M" to designate the marine powerplants, giving rise to the 3M-2500 series engine. Output power of the series (as a whole) proved excellent for the boat class though, as can be expected, natural drawbacks included noise output and high fuel consumption. If running on a consistently full load, the engines could give only up to 6.3 hours of total endurance. During typical usage, PT boat captains managed on one engine to conserve fuel and also preserve the element of surprise. The Packard engine series was progressively uprated with the arrival of the super-charged, water-cooled 4M-2500 (1,200 to 1,500 horsepower) and the final production 5M-2500 of 1,850 horsepower (3 x 1,850 = 5,550 combined horsepower). While Packard was also commissioned to produce the excellent Merlin aircraft engines that powered the famous Supermarine Spitfire fighters of Britain, these were never actually used in ELCO PT boats - instead reserved for the overseas British aircraft demand.
A standard ELCO PT boat of 1943 displaced between 38 to 51 tons with a running length of 80 feet, a beam of 20.75 feet and a draught of just 5 feet - the latter a true tactical advantage if attacked by enemy torpedoes, which require a certain depth of the target under the waterline. Top speed from the combine engine output (concerning the base 1,350 horsepower engine) was approximately 43 knots in ideal conditions. A typical weapons load came to be 4 x 533mm (21-inch) torpedo tubes with 4 x ready-to-fire torpedoes, 1 x 40mm Bofors cannon and 4 x 0.50 caliber Browning heavy machine guns. A typical crew complement was 11 personnel including two officers. By 1945, the later versions of the vessel weighed in at an increased 61 tons and managed a lower top speed of 41 knots. The crew had increased to 14 persons including two officers. However, these systems fitted much more flexible armament arrangements and radar was eventually in widespread use, these installations easily identifiable by the antenna masts (capped with "drum" type installations) at amidships.