Initial delivery to the Air Service was in October 1918, with the aircraft designated
GMB for Glenn Martin Bomber. The first four produced were configured as observation aircraft, and the next two as bombers. Four others were produced before the end of
World War I cancelled all remaining war contracts. The last three aircraft each were configured experimentally, with separate designations:
GMT (Glenn Martin Transcontinental), a long-range version with a 1,500 mi (2,400 km) range;
GMC (Glen Martin Cannon) with a nose-mounted 37 mm (1.46 in) cannon; and
GMP (Glenn Martin Passenger) as an enclosed ten-passenger transport. The GMP was later redesignated
T-1. Six surviving aircraft were later modified and used by the
United States Post Office Department as mail carriers. The design was the basis for the
Martin MB-2, which had a greater load capability but was slower and less maneuverable. Ten aircraft were used by the United States Navy from 1922 under the designations
MBT and
MT and were used as torpedo bombers, two by the Navy and eight by Marine Corps squadron VF-2M. On 5 October 1923, the Marine Corps entered an MT, serial number A-5720, in the
National Air Races in
St. Louis. The aircraft raced with the racing number 58, placing third on the course. They were used in the
West Virginian Coal Wars, notably in the
Battle of Blair Mountain, as bombers and aerial observers sent in by President
Warren Harding. One aircraft was lost, crashing on the return flight, with the loss of three crewmen. ==Variants==