Zastava M55

The Zastava M55, also designated 20/3-mm-M55, is a Yugoslavian/Serbian 20mm triple-barreled automatic anti-aircraft gun developed in 1955 and produced by Crvena Zastava (now Zastava Arms company) in Kragujevac, Serbia, for Yugoslav People's Army use and also for the export market. In addition to the basic towed model M55 A2, the variants M55 A3 B1, M55 A4 B1 and the BOV-3 SPAAG were also developed.
Development.
In 1951, the Federal Secretariat of People's Defense (Serbo-Croatian: "Savezni sekretarijat za narodnu odbranu" – SSNO) 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.
Variants.
Ground model M55 A2.
The standard towed version of the M55 introduced in 1971, is intended for infantry use. The M55 A2 consists of three license-produced, 1.956 mm-long barreled Hispano-Suiza HS.804 20 mm L/70 cannons held in place on a single electronically-powered HSS.630-3 mount and towed carriage for transport. In the driving state, the length is 4.30 m, the width is 1.27 m and the height is 1.47 m. The guns are placed close together to allow quicker reloading and the middle barrel is offset backwards in the horizontal position. The ammunition feed is carried out for each barrel by means of a top-fed 60-round drum magazine. The gun is placed on three foldable feet for use and the wheels are folded up, but it can be fired mounted on the wheeled carriage in an emergency. The suspension is spring-loaded and hydraulically-raised. With the gun, it can be driven to a top speed of 80 km/h; a TAM-110 (4x4) military transport truck is used as a towing vehicle. The total weight, including ammunition is 1,100 kg and without ammunition is 970 kg.
The gunner sits at the rear end of the gun and adjusts the traverse (360°) and elevation (+83° to -5°) with two handrails. It is fired with a pedal. In the M55 A2 B1 improved version introduced in 1975, an automatic optical-mechanical visor (PANS-20/3) is available to the gunner for better target acquisition. The gunner receives various data when the target is detected and the target is advanced; therefore, it is not necessary to keep on firing. With this optics, however, only subsonic aircraft can be engaged. Targets with speeds up to 1,000 km/h can be engaged at a distance of 1,500 m and slower targets up to a distance of 2,000 m. The maximum range for airspace defense is 4,000 m. A theoretical cadence of 700 rounds per minute is possible per tube, although it is able to fire all three guns simultaneously, allowing an impressive rate of fire between 1,950 and 2,250 rounds per minute, which however, cannot be achieved practically due to the reloading times.
In addition to the anti-aircraft role, the Zastava M55 was also used extensively in the direct fire support role, being often mounted on trucks. The operational firing range against ground targets is 2,500 m, the maximum range is 5,500 m.
M55 A3 B1.
This is an improved version of the M55 A2 introduced in 1978. The main difference to the basic model is the hydraulic directional drive of the gun, which is driven by a small gasoline wankel engine to the right of the gunner's seat to provide power and relieve the gunner of having to manually control the traverse and elevation. The engine has an 8 HP performance and 160 cm³, which provides 5.22 kW. With this system a faster judging is possible, the operation is effected by means of a joystick. Total weight is thus increased to 1,235.5 kg with ammunition and 1,150 kg without ammunition. However, the barrels, the mount and the aiming device are identical to the basic model.
M55 A4 B1.
Also introduced in 1977-78, this is an M55 gun system mounted on the towed carriage of the Swiss GAI-D01 anti-aircraft gun. On the A4 B1 a new computer-controlled targeting system – the Galileo ballistic computer – was installed, which automatically monitors the gun after the target has been acquired. In addition, an engine of the same type as the M55 A3 B1 has been placed under the gunner's seat, which was moved from the lateral position found on the previous version in order to improve the weight distribution of the three barrels and prevent them from vibrating. When the cannon is put into position, the towed carriage is removed, and a small splinter-proof shield has been installed in front of the targeting device and the gunner.
M55 A4 M1 (BOV-3).
First introduced in 1983, the BOV-3 SPAAG consists on a modified A4 B1 system upgraded with the Galileo J171 ballistic computer, mounted on a turret installed in the top roof of a BOV armoured personnel carrier.
Combat history.
Africa.
The Zastava M55 A2 was employed extensively by the People's Armed Forces of Liberation of Angola (FAPLA) during the Angolan Civil War (1975-2002) and the later stages of the South African Border War (1966-1990), with a number of them being captured by the South African Defence Force (SADF) during their military operations launched against SWAPO/PLAN guerrilla bases at southern Angola in the 1980s. Some of the captured guns were subsequently stripped from the triple mounts and re-mounted on the Casspir APCs employed by the Koevoet on their counter-insurgency operations in Angola and South West Africa whilst others were handed over to the Armed Forces of Liberation of Angola (FALA), the armed wing of UNITA.
The Zastava M55 was also employed by the People's Forces of Liberation of Mozambique (FPLM) during both the Mozambican Civil War (1977-1992) and the later phase of the Rhodesian Bush War, with a few guns falling into the hands of the Rhodesian Security Forces in the course of their covert cross-border raids ('externals') on Zimbabwe African National Liberation Army (ZANLA) guerrilla training camps in Mozambique during the late 1970s.
Middle East.
Lebanon received from Yugoslavia an unspecified number of Zastava M55 A2 autocannons sometime in the early 1970s, which were assigned to the air defense units of the Lebanese Army and the Lebanese Air Force. These were extensively employed during the Lebanese Civil War (1975-1990), with several guns falling into the hands of the various competing Christian and Muslim militias after the collapse of the Lebanese Armed Forces (LAF) in January 1976. Main operators included the Army of Free Lebanon (AFL), Lebanese Arab Army (LAA), Al-Tanzim, Kataeb Regulatory Forces (KRF), Zgharta Liberation Army (ZLA), the Tigers Militia, The Arab Socialist Union (ASU), the Druze People's Liberation Army (PLA) and the Al-Mourabitoun, who mounted their Zastava M55 autocannons on technicals and M113 armored personnel carriers.
Yugoslav Wars.
During the breakup of Yugoslavia and the subsequent Yugoslav Wars that erupted in the 1990s, both the Zastava M55 towed versions and the BOV-3 SPAAG were employed extensively in the Ten Day War in Slovenia, the Croatian War of Independence, the Bosnian War and the Croat-Bosniak War by nearly all the warring factions. These included the Yugoslav People's Army, the Army of the Republic of Serb Krajina and the Army of Republika Srpska on one side, and their adversaries of the Slovenian Territorial Defence, the Croatian National Guard, the Croatian Defence Council and the Army of the Republic of Bosnia and Herzegovina on the other.
2020 Nagorno-Karabakh War.
Azerbaijan's Ministry of Defence reported that it had destroyed two Armenian Zastava M55s between the 9th and 10th of October 2020 as part of the 2020 Nagorno-Karabakh war.