Manufactured by the Glenn L. Martin Company, the XPB2M-1 Mars (Model 170) was developed as a prototype for the U.S. Navy in 1938 as a long-range patrol flying boat. This was converted in 1943 into a transport aircraft, designated the XPB2M-1R Mars (Model 170), which involved the addition of additional cargo hatches and cargo loading equipment as well as enlarging of the existing hatches and the removal of armament. Flight testing on the XPB2M-1R began in May 1943 and ended with a 33 hour endurance flight in October of that year. The Navy accepted the aircraft in November 1943. In 1944, the Navy ordered additional transport aircraft that were delivered between 1945 and 1948 as five Martin (Glenn L.) JRM-1 Mars (Model 170A) aircraft and one Martin (Glenn L.) JRM-2 Mars (Model 170B). The Mars was the largest Allied flying boat to enter production. Frederick C. Phillips was an engineer at Glenn L. Martin Company and served as an observer on the Martin (Glenn L.) (JRM) XPB2M-1R Mars (Model 170) endurance flight in October 1943.