XTN-1, SDW-1, CS-1, CS-2, SC-1, T3M-1
A twin-engine biplane was ordered from the Naval Aircraft Factory in May 1925 and three more designed to the same BuAer specification were assigned to Douglas in July. The first Douglas XT2D-1 was flown January 27, 1927, at Santa Monica with wheels, and the NAF XTN-l was completed in May. Both had two air-cooled 500-hp Wright P-2 radials, folding wings and a narrow fuselage with three cockpits.
A 1,628-pound Mk 7 torpedo or bombs was carried between twin floats, which could be exchanged for wheels. The Douglas XT2D-l joined VT-2 at San Diego in May 1927, and was the only twin-engine aircraft actually intended for tests on the Langley. These trials were canceled when the
P-2 proved unreliable, and had to be replaced by 525-hp Wright R-1750 Cyclones with three-blade propellers.
Nine more T2D-ls ordered from Douglas had a balanced rudder and four cockpits. Delivered in 1928, they did most of their service on floats at Pearl Harbor, since the Navy decided that carrier deck space was better used by larger numbers of single-engine types.
Eighteen more Douglas twin-engine aircraft were ordered on June 12, 1930, with R-1820E Cyclones, more fuel and twin rudders. By the time they were delivered, shore-based torpedo units had been redesignated as Patrol squadrons, for land-based attack was held an Army mission. Designated P2D-l, the Douglas ships were completed by June 1932 and served with VP-3 in the Canal Zone until replaced by PBYs in February 1937. Armament comprised two flexible Brownings, a torpedo, or bombs.
Three Men, Two Wings, and a Torpedo
Such a type was available in the Martin T3M-1, 24 of which were ordered October 12, 1925, and entered service with VT-l in September 1926. A development of the SC-2 (T2M), it had the same short upper wing, a 575-hp Wright T-3B, and an all-welded steel tube fuselage framework, with the pilot and torpedo-man seated side-by-side ahead of the wing. A gunner in the rear cockpit had a Scarff ring and a floor opening for his Lewis guns. Twin floats or wheels were interchangeable as landing gear.
One hundred T3M-2s with a 710-hp inline Packard 3A-2500, equal-span wings, and three seats in tandem, began appearing by February 1927 and equipped the first squadron (VT-l) to go aboard the Lexington after its commissioning in December. This meant the Navy carried its aerial punch to sea, but few realized that an actual substitute for battleships was appearing. VT-2 also flew from the Saratoga ‘s deck, while VP-2D, VT-3D, and VT-4D at Coco Solo, VT-5A with the Asiatic Fleet in the Philippines, VT-6 and VT-7 at Pearl Harbor, and VT-9 on the Wright, usually operated the T3M-2 on floats. NAS Pearl Harbor also flew the twin-engine T2D-ls of VP-1D.*
These biplanes used water-cooled inline engines, but development of the air-cooled Pratt & Whitney Hornet radial provided a lighter power plant and reduced empty weight by a third. This engine was tested on the XT3M-3, converted from the first T3M-2, and also used on the XT4M-1 (Martin Model 74), a prototype first flown in Cleveland on April 27, 1927, with the previous wooden structure replaced by a new folding-wing metal framework covered by fabric.