In the early 1960s, the German Air Force became increasingly concerned that its airfields were vulnerable to air attack from Eastern Bloc forces and actively researched the possibility of dispersed operations which included flying from Autobahnen (Motorways). Although feasible it would still require aircraft with STOL capabilities. At that stage the German Air Force was equipped with F-104 Starfighters. A plan was put afoot that involved the modification of the Starfighters to be rocket-launched from stationary ramps and to be recovered from short strips using aircraft carrier-type arresting gear.
The Do 31, a West German experimental VTOL jet transport built by Dornier was intended to use the same strips as forward operating bases. The Do 31 was designed to meet a NATO specification (NBMR-4) for a tactical support aircraft for the EWR VJ 101 VTOL strike aircraft designed under the NATO contract of BMR-3.
Initial designs incorporated a Bristol Pegasus vectored-thrust turbofan in each of the two inboard nacelles and four Rolls-Royce RB162 lift engines in each of the outer nacelles. It was planned to dispense with the outer nacelles and their engines when the larger RB153 became available. By mounting the engines in pods, the fuselage could provide a capacious hold with a rear loading ramp.
In all, three test prototypes were built. E1, the first prototype designed to test horizontal flight powered by two Pegasus engines first flew on 10 February 1967. E2 was a static test airframe. E3 had both Pegasus and RB162 lift engines installed and was designed to test the vertical flight mode. with just the two Pegasus engines. The third prototype (E3) flew in July 1967 with all ten engines fitted. The first hovering flight took place on 22 November 1967. Full forward and backward transitions were made in December 1967.
The Do 31 established several Fédération Aéronautique Internationale (FAI) world records during its ferry flight to the 1969 Paris Air Show.
When the high cost, technical and logistical difficulties were realised, the German Air Force ceased trials involving VTOL aircraft which resulted in the cancellation of these projects in April 1970, although it made its final public flight on 4 May 1970.