The Marquardt Company was set up in 1944 for the purpose of study work into subsonic ram-jet engines. The company has since developed 50.8-centimetre diameter ram-jets capable of supplying power equivalent to 2500hp. A Lockheed F-80 "Shooting Star" fixed-wing aircraft was fitted with this ram-jet and during trial flights was powered solely by it, the normal power source having been switched off.
Development work has also been done on other ram-jet engines as well as on pulse-jet engines to equip target drones.
Marquardt has also produced a helicopter powered by two pulse-jet engines 20.4 centimetres in diameter. This helicopter, a simplified structure in steel tubing, was intended to act as a flying test bed for the pulse-jet engines developed by the Marquardt Company. At each tip of the two-bladed rotor were located the above-mentioned pulse-jet engines. Directional control was ensured by means of a rudder. The M-14 was the first American helicopter to have flown on power provided by two pulse-jet engines.
P.Lambermont "Helicopters and Autogyros of the World", 1958