The M-84 is based on the Soviet T-72 but with several improvements, including: a domestic fire-control system, improved composite armor, and a 1000-hp engine. The M-84 entered service with the Yugoslav People's Army in 1984. The improved M-84A version entered service a few years later.
In the late 1980s, a project for a replacement tank called the M-91 Vihor (Whirlwind) was started. Unlike the M-84, the Vihor was not a copy of a Soviet tank, but a new design from scratch. Two prototypes were created by 1991. One was completely finished, but the factory refused to deliver it to the Yugoslav People's Army. The second prototype only had its body completed. Due to the disintegration of Yugoslavia, the M-91 project was paused until the end of the civil war in Croatia. After 1994, the second tank body was fitted with a new turret and the entire project was renamed Croatian main battle tank M-95 Degman. The M-95 Degman is still in prototype phase.
Croatia also created an M-84D Degman upgrade package for the M-84. The Croatian army planned to upgrade its 75 M-84 tanks to the M-84D revision, but due to the economical crisis, the upgrade was postponed.
The latest Serbian version of the M-84 is the M-84AS, unveiled in 2004. It features a new fire control system, Kontakt-5 ERA armor, AT-11 Sniper anti-tank missiles, Agava-2 thermal sight, and the Shtora defensive suite. It is very similar to the Russian T-90S, both in appearance and in capability.
About 150 M-84 tanks were exported to Kuwait. The disintegration of Yugoslavia in the 1990s prevented further exports of the M-84. ASELSAN of Turkey was selected by Kuwait to modernize their M-84s
The M-84A is armed with a 2A46 125 mm smooth bore cannon. The gas cylinder positioned in the middle of the barrel is shielded with a thermal coating that minimizes deformation of the barrel from high temperatures and ensures it is cooled at the same rate during rapid firing. The M84 uses an automatic loader, which enables it to sustain a firing rate of 8 rounds per minute.
The cannon's ammunition is stowed underneath the turret (40 rounds) within the hull of the tank. This concept was inherited from the original Soviet design for T-72 and is arguably the tank's greatest flaw. While it enables fast rates of fire, it also makes the M-84 vulnerable. This weakness was exploited by Croatian soldiers in the Croatian War of Independence to the detriment of the YPA's tank crews. In later stages of the conflict, losses were reduced by adjusting and improving tactics.
Along with its primary armament, the M-84 is also armed with one 7.62mm coaxial machine gun, and one 12.7mm anti-aircraft gun mounted on the commander's turret.
All versions of the M-84 have a crew of three. The commander sits on the right side of the turret, the gunner on the left, and the driver sits centrally at the front end of the vehicle. Like most Soviet derived vehicles, the M-84 series of tanks do not have a manual loader, due to the tank's autoloader system.
The armour of the M-84AS tank consists of cylindrical pad, high-hardness steel, titanium, tungsten, aluminium as well as modular Kontakt-5 reactive armour plates. Croatian M-95 Degman versions use improved armor protection with four layers of titanium, two layers of tungsten and three layers of ceramic armor giving protection of 592 mm against HEAT, APSF and Chemical attacks. In addition to this, the Degman is extensively covered with explosive reactive armour plating.
Twelve smoke grenades are positioned in front of the turret in banks of five and seven grenades. Thermal imaging and infrared guidance are positioned on the top-right side of the turret. The M-84 has a search light used in short-range combat situations.
The M-84 tank has nuclear, biological and chemical (NBC) protection capabilities.
The base M-84 engine is a 12-cylinder water-cooled V46-6 diesel engine, rated at 574 kW. The improved M-84A has a more powerful, V46-TK 735 kW (1,000 hp) engine. With maximum fuel capacity (1,200 litres) the tank's range is 450 km, and with external fuel tanks, this range can be extended to 650 km.
The Croatian-made variants have enhanced power plants. The M-84A4 Sniper model has a German-built 820 kW (1,100 hp) engine, while the M-84D has a 895 kW (1,200 hp) engine, the most powerful of all M-84 variants. The M-84D also has greater fuel capacity (1,450 litres).
The tank can ford 1.2 meters of water at any time, or up to 5 meters with a proper snorkel applied.