In the summer 1939 an engineer I.Merkulov offered the use of ramjet (PVRD) as the additional power installation for increase of maximum speed of fighters with piston engines. The air petrol from a main tank was poroposecl to be used as fuel. The first engine, that received a designation DM-1, passed bench tests in the second half of 1939. In September more powerful engines DM-2 were made, their length was 1500 mm, maximum diameter 400 mm, diameter of the output nozzle 300 mm. The weight of each engine together with fastening was only 62 Ib. In September 1940 DM-2 were mounted on 1-153 fighter resulting in a gain of speed of 18.6 mph. In October same year DM-4 engines were tested on Tchaika. At turning on of DM-4 the speed of a plane was increased by 25-31 mph. In total 74 test flights were completed using DM-2 and DM-4 engines.
