Thomas - Morse MB - 3 The Thomas - Morse MB - 3 was an open - cockpit biplane fighter primarily manufactured by the Boeing Company for the U . S . Army Air Service in 1922 . The MB - 3A was the mainstay fighter for the Air Service between 1922 and 1925 . Development . In March 1918 , the United States Army Air Service requested several American aircraft manufacturers to design a new fighter , to be powered by a Wright - Hispano H , a license - built Hispano - Suiza 8 , to replace the French - built SPAD XIII . The Thomas - Morse Aircraft Corporation of Ithaca , New York proposed the MB - 3 , designed by its British - born chief designer B . Douglas Thomas , to meet this requirement , with an order for four prototypes being placed in September 1918 . The MB - 3 was a single seat two - bay biplane of similar layout to the SPAD XIII that it was intended to replace . It was of wood and fabric construction with a fixed conventional landing gear . Powerplant was the expected Wright - Hispano water - cooled V - 8 engine driving a two - bladed propeller and cooled by a radiator mounted on the center - section of the upper wing . The pilot sat in an open cockpit under a cut - out in the upper wing , with two 0 . 30 in Marlin machine - guns mounted ahead of the pilot . The first MB - 3 made its maiden flight on 21 February 1919 . Testing showed that the fighter had good performance and handled well , but the cockpit was cramped and gave a poor view for the pilot . The prototypes were plagued with fuel leaks and suffered serious engine vibration , while maintenance was difficult , often requiring holes to be cut in the fuselage structure to allow access . Despite these problems , the Air Service was sufficiently impressed with the MB - 3 to place an order for 50 aircraft with Thomas - Morse in June 1920 . The Air Service had a requirement for more fighters , and issued a request for tenders for a further 200 of a modified version of the MB - 3 , the MB - 3A , which incorporated a number of changes developed by the Air Service as a result of testing at McCook Field , including a stronger structure and replacing the wing - mounted radiator with ones on each side of the fuselage in - line with the cockpit . Thomas - Morse was confident in winning orders for the MB - 3A , investing in the necessary jigs for such a large production order , but was heavily underbid by Boeing , whose mass production methods allowed it to profit while still charging a lower price ( in the case of the MB - 3A , $ 7 , 240 per copy ) , saving almost half a million dollars over the 200 aircraft contract , awarded on 21 April 1921 . Boeing credits this contract with rescuing the company from financial difficulties following the cancellation of orders after World War I , and with being the impetus for its rise as a premier manufacturer of military aircraft . Thomas - Morse did manage to win a contract for 12 MB - 3s for the US Marine Corps in May 1921 , with the order later being changed to substitute two MB - 7 racing aircraft , a MB - 3 with the biplane wings replaced by parasol wings , for two MB - 3s , with a further MB - 3 purchased when one of the MB - 7s crashed . Additionally , the Army ordered three MB - 6 , another racing version of the MB - 3 with shorter span wings and a more powerful engine in May 1921 . Operational history . Two of the prototypes were entered in the 1920 Pulitzer Trophy race , with one finishing in second place behind the Verville VCP - R , completing the course in an average speed of . Completed MB - 3s started to roll out of Thomas - Morse ' s factory in April 1921 , but deliveries were delayed by an accident during testing when an MB - 3 lost a section of the upper wing during diving tests , this causing the type to be grounded while the accident was investigated . The 1st Pursuit Group began to receive MB - 3s in January 1922 , supplementing its elderly SPADs and S . E . 5a s . In service , the new type was troublesome , being unreliable ( over a ten - day test period in May 1922 , the number of servicable MB - 3s dropped from 20 out of 36 to just 3 ) and continuing to suffer the vibration problems encountered by the prototypes , eventually traced to the rigid engine mount . The first delivery of the improved MB - 3As took place on 29 July 1922 , with the last aircraft delivered on 27 December that year . The last 50 MB - 3As were fitted with larger tail surfaces . As well as allowing re - equipment of the four squadrons of the 1st Pursuit Group , the MB - 3As were issued to a number of overseas squadrons , equipping two squadrons on Hawaii , one in the Philippines and one in the Panama Canal Zone . From 1926 , the MB - 3A started to be replaced by the Curtiss PW - 8 and Boeing PW - 9 fighters . A number of aircraft were refurbished and used as MB - 3M advanced trainers at Kelly Field , remaining in use until 1929 . The Marine Corps took delivery of its MB - 3s in February – March 1922 , but the type was unpopular with the Marines , being withdrawn from use in July that year and sold back to the Army for use as MB - 3M trainers .