After a Thomas-Morse MB-3 finished second[2] at the 1920 Pulitzer Trophy air race, the Army asked Thomas-Morse to build a new aircraft for the 1921 race.

The MB-6 was a redesigned MB-3, with a reduced wingspan and 400 hp (300 kW) Wright H-2 engine.

The three aircraft arrived for testing at McCook Field on 20 September 1921.

Mccready, it came in third behind two Curtiss aircraft, with a speed of 160.71 mph (258.64 km/h).

The aircraft was given the military designation R-2 in 1922 and scrapped on 31 October 1924.