In 1951, the Federal Secretariat of People's Defense of Yugoslavia purchased the manufacturing licence of the single-barrel Hispano-Suiza HS.804 20mm L/70 anti-aircraft autocannon mounted on the HSS.630-3 towed gun carriage.
The HS.804 entered production by the Crvena Zastava Company in 1955 as the Zastava 20/1mm M55 and the Company's engineers began working in the development of a triple-barrelled version. In 1971 the first prototype of the triple-barrelled Zastava 20/3mm M55 was completed, which entered production that same year.
20 mm M71 weapon is fitted with an automatic 20/1mm M55 gun fed with ammunition from easily replaceable drums with the capacity of 60 rounds. Automatic 20/1mm M55 gun has been adapted to enable installation onboard ship:
The cannon and the ammunition feeding drum are turned (the drum is on the bottom side) and are protected with the cradle and case collector against water splashing (sea or river);
Hydraulic shock-absorber is adapted so as to enable smooth automatic operation of the gun
The gun is triggered by the right hand forefinger. The firing bar has a reliable effect at all elevation angles, and accidental triggering is prevented with a brake located on the weapon cradle.
The gun is fitted with a firing stop which profiles the action zone in accordance with the allowed action sectors (bearing in mind protection of the ship superstructure).
20 mm M75 is a quadruplely coupled M71, equipped with devices to synchronize fire. So You
@TIGREDELAIRE have a lot of reasons to claiming that this is a family of weapons similar to M55.
Envío saludos cordiales desde Polonia.
