T2D-1, P2D-1, T3M-l, T3M-2 XT3D-1
Production T4M-ls first ordered June 30, 1927, appeared in April 1928 with a larger, balanced rudder, and were armed with two Lewis guns, a Mk 7 torpedo, or three 500 or 12 100-pound bombs. Three tandem cockpits were provided for the observer, pilot, and gunner, with room inside for a fourth man to operate the radio, or fire a gun at the floor opening. By then the Navy had the 1,740-pound 2A version of the Mk 7 torpedo, but the long, slow, launching run still put the torpedo plane at great risk to enemy guns.
The Navy put 102 T4M-ls into service, beginning in August 1928 with VT-2B on the Saratoga. The Lexingtonís VT-lB also got the T4M-l, while twin-float versions were used by VT-9S, usually working in the Atlantic with the tender Wright.
Glenn L. Martin decided to move his firm to Balti≠more, Maryland in 1929, and sold his old Cleveland, Ohio plant to the Great Lakes Corporation, which received a Navy contract June 25, 1929, to continue torpedo-plane production. Eighteen TG-l biplanes were similar to the T4M-l, but for an R-1690-28 Hornet, modified landing gear and folding wings. The first TG-l was tested at Anacostia in April 1930 with twin floats and armed with a torpedo or 1,000 pounds of bombs, two Lewis flexible guns on the rear cockpit ring, and a fixed .30-caliber Browning in the upper wing, the first forward gun on a single-engine torpedo type. Most TG-ls went to VT-2, beginning in June 1930, with tail hook, main wheels with brakes, and new tail wheels.
A Wright R-1820-86 Cyclone powered the Great Lakes TG-2 that had two .30-caliber flexible Brownings, one in the rear cockpit, and the other in the front cockpit with a guard rail to protect the propeller when the gun moved. The fixed gun was deleted. Thirty-two TG-2s were ordered July 2, 1930, and delivered from June to December 1931, serving on the Saratoga with VT-2 until replaced by TBD-l monoplanes late in 1937.
During most of this time VT-2 was the only torpedo plane squadron in service, for the shore-based units had become patrol squadrons and VT-1 replaced its T4M-1s with BM-1 dive-bombers. Until development of a new weapon, the Mk 13, which could be dropped from faster and higher attacks, the torpedo was less effective than dive-bombing.
There were two efforts to design a TG-2 replacement, the first being Martinís XT6M-1 ordered June 28, 1929, and completed in December 1930 as an all-metal, long-nosed biplane with a Wright Cyclone, a fixed upper wing gun and two Lewis guns. This was a two-seater specialized for torpedo work, but the Navy was losing faith in that weapon. It had no more success than the three-place Douglas XT3D-1, ordered on June 30, 1930, and tested in October 1931 with a 575-hp Hornet B single-row radial and a flexible Browning in the rear cockpit. The front cockpit also had a flexible gun, and the bomber window facing forward indicated the greater emphasis on level bombing, instead of torpedoes. In May 1932 this aircraft was returned to Douglas for installation of an 800-hp twin-row XR-1830-54.
Redesignated XT3D-2, it reappeared in January 1933 with a NACA cowl, wheel pants, and low enclosures for the three crewmen. Badly streamlined, was the official verdict, and no production orders were placed. On March 28, 1935, a Norden Mk XV bombsight and automatic pilot was installed to demonstrate the new Stabilized Bombing Approach Equipment (SBAE) system planned for the new PBY and TBD types. Weighing 178 pounds for that trial, this bomb aiming system would become most famous when used by the Army Air Force heavy bombers in World War II.