The Martin T4M was a version of the earlier T3M torpedo bomber, powered by a Pratt & Whitney Hornet engine.
The T3M was itself developed from a Navy design that had originally been produced by Curtiss as the CS-1 and CS-2, before Martin won the main production contract, building it as the SC-1 and SS-2. All four of these aircraft were basically identical three man biplanes, with open cockpits for the pilot and gunner and an internal position for the bomber/ torpedo man, an unusual configuration with a longer lower wing and powered by Wright T-2 or Wright T-3 engines. The aircraft was designed to operate on wheels or as a float plane, and for it to be possible to change between the two quickly.
In November 1924 one of the CS-2s was given a geared Wright T-3 engine, becoming the CS-3. Martin then improved the overall design, which entered production as the T3M. A total of 124 T3Ms were built, making it the most numerous member of the overall family.
One T3M was used to test out alternative engines, becoming the XT3M-3 when powered by a Pratt & Whitney R-1690 Hornet and the XT3M-4 when powered by a Wright R-1750 Cyclone. This encouraged the Navy to order a new prototype using the Hornet engine. This became the Martin Model 74, or the XT4M-1 prototype, which was powered by the R-1690 Hornet. This aircraft made its maiden flight in April 1927.
The XT4M-1 was ordered into production as the T4M-1, with the first contrast placed on 30 June 1927. This used the Pratt & Whitney R-1690-24 Hornet radial engine, and 102 were produced in 1927-8. It had shorter wings and an revised rudder, and was almost always used with wheels as a carrier based aircraft.
The wheeled version of the T4M-1 served on the USS Lexington (VT-2B) and USS Saratoga (VT-1B), alongside the T3M-2. The T4M-1 remained in service with Reserve units into the mid 1930s.
To add to the confusion, Martin then sold their Cleveland factory to the Great Lakes Aircraft Corporation. This company continued to build the T4M. Eighteen were built as the Great Lakes TG-1, powered by the R-1690-28 Hornet engine, making it similar to the T4M.
Another 32 were built as the TG-2, powered by the Wright R-1820-56 Cyclone, an improved version of the R-1750 Cyclone that had been used in the single XT3M-4 prototype. This improved its top speed, climb rate and service ceiling, but did slightly reduce its range. The TG-2 remained in service with VT-2 until 1937, making the last member of the family to be in front line service.
Great Lakes also attempted to produce a civilian version of the T4M, building two examples of an eight seat passenger aircraft named ‘Miss Great Lakes’. No orders followed.
The T3M and T4M were followed in service by the Douglas TBD-1, marking the change from biplanes to all-metal monoplanes.
Engine: One Pratt & Whitney R-1690-24 Hornet radial engine
Span: 53ft 0in
Length: 35ft 7in
Height: 14ft 9in
Empty Weight: 3,931lb
Take-off Weight: 8,071lb
Maximum Speed: 114mph at sea level
Cruising Speed: 98mph
Climb rate: 14min to 5,000ft
Range: 363 miles
Guns: One 0.3in machine gun on Scarff ring mount
Bomb load: One torpedo