Vihor M-91

Socialist Federal Republic of Yugoslavia (1985-2000)
Main Battle Tank – At Least 3 Incomplete Prototypes Built

Throughout its existence, the Jugoslovenska Narodna Armija (JNA, English: Yugoslav People’s Army) strove to develop a domestic tank design in order to break its dependence on foreign suppliers. The initial projects involved either reusing already available components or simply improving an available design. None of these ever reached beyond the prototype stage. The first successful locally-produced tank, although a licensed copy, was the M-84, which entered service in the second half of the 1980s. Despite being a competent design, the Yugoslav Military High Command wanted an even better-performing tank, which would lead to the Vihor project.

The First Attempts to Build a Domestic Tank

Following the end of the Second World War, the JNA entered a short period of close cooperation with the Soviet Union. This cooperation is reflected in the procurement of large quantities of military equipment, including tanks, such as the T-34-85. While the JNA was still in its early development phase, political tensions between Yugoslavia and the Soviet Union, more precisely between Tito and Stalin, began to arise. Stalin wanted to impose a more direct Soviet control of Yugoslavia, as in the other satellite Eastern European states, something that Tito fiercely objected to. This led to Tito’s famous ‘no’ to Stalin, the so-called Tito-Stalin Split, in 1948, which basically isolated Yugoslavia from the Eastern Bloc. The situation became even more critical as Yugoslavia’s eastern borders were surrounded by the Soviet allies. The possibility of a Soviet invasion was a real threat to Yugoslavia at that time, as the examples of Hungary in 1956 and Czechoslovakia in 1968 showed.

The JNA, at this point, was in a quite precarious situation. The Army was in the process of reorganization and rearmament and was heavily dependent on Soviet military supplies. The problem also resided in the fact that the Western powers initially refused to deliver any military support to Communist countries. One way to resolve the dependence on foreign aid was to introduce domestic tank production. The production of domestically developed tanks was something that the JNA was obsessed with. This was, at that time, an almost impossible task. It required a well-developed industry, experienced engineering staff, and, probably most importantly, time, all of which Yugoslavia lacked at that moment. The industry and its infrastructure were almost destroyed beyond repair during the war. Many specialized workers were either killed or displaced across Europe and the fact that the Germans took almost all machine tooling and equipment with them did not help either.

Nevertheless, in 1948, work on such vehicles was initiated. The Petar Drapšin workshop was instructed to produce 5 prototype vehicles. The new tank was designated simply as Vozilo A (English: Vehicle A), also referred to sometimes as Tip A (English: Type A). In essence, it was to be based on the Soviet T-34-85 tank with improved overall characteristics. While it used the same gun and the suspension, the superstructure and turret design were greatly changed.

While the 5 prototypes were completed, they quickly showed a number of deficiencies. Most of these were due to inexperience, lack of adequate production capacity, and more importantly, the fact that there were no design plans. All five tanks were generally different in detail from each other. For example, some were heavier by a few hundred kilograms. When the JNA field-tested these vehicles, it was not possible to make an accurate assessment of their capabilities. They could not be considered as prototype vehicles for possible future production. In order to get any useful information, it was necessary to produce several more vehicles, which were deemed too expensive. This led to the cancellation of this project.

While the Vehicle A project was canceled, in the years that followed, the JNA would conduct a series of different projects aimed at either developing a new vehicle by using existing components from available tanks or improving the performance of those vehicles that were in service. This led to a series of different experimental designs, such as the self-propelled Vozilo B (English Vehicle B), M-320, M-628 ‘Galeb’ (English: Seagull), and M-636 ‘Kondor’ (English: Condor), etc. These mostly included components from different existing tank designs, such as the Soviet-designed T-34-85 or the US-designed M4 Sherman and M47 Patton tanks. With a better relationship with the Soviet Union in the 1960s, T-54s and T-55s began to arrive in increasing numbers. The JNA initiated a project to locally produce a copy of the T-55 under the name T-34D. In the end, besides a few prototypes, nothing came from these projects. The reason for this was the inability of the Yugoslav industry to produce these tanks. At the same time, it was deemed cheaper to simply buy the new equipment from aboard. Ultimately, work on these would be suspended during the 1960s.

The First True Domestic Tank – the M-84

For more than a decade, there were no attempts to develop a domestic tank design. After a long and exhausting negotiation with the Soviets, the JNA finally managed to purchase a license for the production of the T-72 Main Battle Tank (MBT) in 1978. The first prototype (possibly two) was finished in 1979. As the first T-72 tanks began to be produced, the JNA military hierarchy wanted to go further by developing a new improved design. While it was to be heavily based on the T-72, the new project was to incorporate nearly 60% of newly developed parts and components (tracks, electronic installation, improved engine, protection, etc). This would lead to the creation of an initiative known as T-72MJ, later renamed to M-84, of which some 650 tanks would be built in a few different versions.

The Vihor Project

When the M-84 entered service, it was deemed a good design. More importantly, it fulfilled the decade-long dream of the JNA’s Military High Command of producing a domestic tank. Still, it was theorized that even this tank would eventually become obsolete and that the tank technology regarding protection, armament, and speed would progress further.  Thus, as the M-84 production was underway, the Glavni Vojnotehnički Savet (English: Chief Military Technical Council) initiated a new tank project designated as ‘Zadatak Vihor’ (English: Task Whirlwind).

The new tank was to have improved firepower, mobility, and protection to rival that of other modern tank designs in the world. To speed up the development time, the most advanced components of the existing T-72 and M-84 tanks were to be reused. Despite this, it was to be quite different from these two tanks.

In order to gain a better grasp of the new tank technologies, a JNA military delegation would be sent to a couple of countries around the world. In early 1985, one of the first countries visited was France and Ateliers de construction d’Issy-les-Moulineaux (AMX) tank manufacturer. The JNA delegation was presented with the new development of the AMX armor plates. The French engineers were highly interested in the T-72’s performance. The JNA officials were especially interested in the AMX engine developments and talks were initiated on the possible purchase of the V8X 1,000 kW engines. While serious negotiations were undertaken, for unspecified reasons this was never realized.

Egypt and China were also visited. As the Egyptian tank industry was modest, not much was learned there. China was more promising and the JNA delegation had the chance to see the Type 59, but otherwise, no deals were made. In the US, the JNA delegation visited the TACOM military center near Detroit in mid-1985.

Lastly, the United Kingdom was visited in 1986. At that time, the United Kingdom’s arms industry was in an economical crisis and was more than willing to sell various military equipment. The JNA officials were not keen to purchase any technologies from the United Kingdom as most parts would not fit or were simply too expensive to acquire.

In any case, the first drawings and calculations of what would become the new tank were completed in 1985. As no major issue was found with the first drafts, the project got the green light, and work on the first prototype began in 1987. The completion of the prototype stage was to be achieved by the end of 1994 or 1995, with a production of some 15 trial vehicles. If all went without a problem, a yearly production order of 100 vehicles was to be given. The production run was to begin in 1996 and end in 2012. This vehicle was to replace the T-55. The first pre-prototype vehicle was completed in 1989 and given to the Yugoslav Army for testing. However, this would never be close to achieving.

Name

The first prototypes received the OBV A-85 designation. The production vehicles were to be known as Vihor M-95. In various sources, this vehicle is also known as either Vihor M-90 or M-91. The practical naming convention of the vehicles in JNA service was closely related to the year of introduction. Given that it was estimated that this vehicle would enter production in 1995, the M-95 designation (not to be confused with the Croatian development project with the same name) may seem appropriate. To avoid any confusion, this article will refer to it simply as the Vihor.

Vihor Design

It is important to note that the Vihor was in the early experimental development state, so much of its overall performance is not known with total certainty. If the development process was fully completed, new changes may have been implemented or discarded.

Chassis 

The overall Vihor hull was rather simple in its design. It could be divided into three sections. The front part, where the driver was positioned, was protected with a simple but steep angled armored plate. In the center, the turret with its main armament was positioned. Lastly, to the rear, the fully enclosed engine compartment was located. Its construction was made by welding mostly flat armored plates, with the exception of the front part. The Vihor hull design was more or less a direct copy of the M-84. To the front, there was a hatch for the driver that opened to the right side. The engine compartment was covered with a much larger access hatch.

Engine

The Vihor was to be powered by the B-46-TK-1 1,200 hp engine. This engine was an improved version of the engine used on the modified M-84A/AB, the 1,000 hp V-46TK engine. The power ratio in this vehicle was 27.2 hp per tonne. In comparison, the T-72 had a power ratio of 18 per tonne, while the Abrams (depending on the variant) ranged between 23 to 26 hp per tonne. It received two turbochargers with an exhaust air cooling system.

Two sub-versions of this engine were proposed, one using components imported from abroad and a second variant with domestically developed parts. The engine could effectively work at temperatures ranging from -30°C to +53°C. This was a potentially great chance for export around the world.

With a vehicle weight of only 44 tonnes, the maximum speed achieved was 75 km/h. This speed even slightly exceeded the expectations and calculations made prior to its testing. Acceleration from 0 to 32 km/h required seven seconds. The transmission was a GC-TRONIC hydromechanical transmission that had 5 forward + 1 reverse gear.

The engine compartment was also cleverly designed to be as small as possible. The engine, with its dimensions of (L-W-H) 153 x 103 x 95 cm, and the transmission assembly took up only 3.4 cubic meters. This greatly aided to reduce the vehicle’s overall dimensions and helped to save weight.

Suspension

The suspension consisted of six road wheels, a rear-drive sprocket, a front idler, and three return rollers. These were suspended using torsion bar units. While more or less a copy from the M-84, there were some differences. Firstly, the Vihor’s roadwheel vertical travel was increased to 350 mm in comparison to 280 mm on the M-84. The road wheels were built using aluminum alloys. The 580 mm wide tracks were built using either steel or a combination of aluminum alloys. Rubber rims could be added to the tracks. The weight of one track assembly was 1,900 kg. When equipped with rubber rims, the weight of these tracks was increased to 2,300 kg.

Turret 

The original electrohydraulic traverse system was replaced with an electromechanical one. Thanks to this system, the turret’s horizontal rotation speed was 20°/s, so it swung 360° in 18 seconds. In contrast to the generally round-shaped turret used on the M-84 and T-72, the Vihor received a quite different design. While the front was quite similar, the rear of the turret was redesigned and extended. The extra free space was used to store the radio and other equipment. On top of the turret, there were two escape hatches for the turret crewmembers. The one on the left was for the gunner and the one on the right for the commander. Various equipment and storage boxes were to be externally mounted on the turret sides.

Inside the turret, the radio equipment was located to the rear. This was an encrypted, frequency hopping radio with 16 programmed channels and a frequency range of 30 to 87.9 MHz. The command vehicles were to be equipped with additional radio equipment.

Armament and Ammunition

For the main armament, the 125 mm 2A46M smoothbore gun was chosen. This was the basic armament of the M-84 tank and Soviet-built MBTs such as the T-64 and the T-72. Given its availability and general effectiveness, it was logical to reuse this gun for the Vihor project. The difference was that it would have received a number of improvements and modifications to further increase its effectiveness and durability. These included adding a muzzle reference system (MRS) for measuring gun barrel curvature, thermal insulation lining of the barrel, using better raw materials for the production and improved production techniques for its construction, and testing a new quick-change mechanism, among others. The gun was to be provided with horizontal and vertical stabilization during the acquisition of targets. In order to help the crew with targeting, the Vihor was to be provided with advanced electronic ballistic computers.

The Vihor fire control system was a complex unit consisting of many elements, such as the day/night sight. Another interesting device with which the Vigor was equipped was a display for the commander connected to the gunner’s sight. This permitted the commander to see the targets that the gunner was aiming at. The Vihor was also equipped with thermal imaging with a magnification of 8x to 10x, a laser range finder, third-generation night vision, a laser-warning receiver connected to the externally mounted smoke launchers, etc. The electronic ballistic computer could be used to enter all necessary information regarding the target.

The electro-mechanical autoloader was basically the same as the one used in the M-84. This autoloader was located under the turret, on the tank’s floor. It held 22 rounds in its rotating transporter. An additional 18 rounds were to be stored inside the crew compartment. With these and other various improvements (like adding a bidirectional movement autoloader), the rate of fire was estimated to be around 10 rounds per minute.

It was requested that the gun, with all its improvements needed, be capable of piercing 400 mm of RHA armor at ranges of 2 km using Armor-Piercing Fin-Stabilized Discarding Sabot (APFSDS) rounds. When using High-Explosive Anti-Tank (HEAT) rounds, it was supposed to be able to penetrate around 600 mm of RHA armor.

Besides the main armament, the secondary armament did not change from the M-84. It consisted of one coaxial 7.62 mm PKT and a turret-mounted 12.7 mm NSVT heavy machine gun. While sources do not mention ammunition load, this would most likely have remained the same as on the M-84. This meant 2,000 rounds for the PKT and 300 rounds for the NSVT heavy machine gun.

Armor and Protection

The Vihor would have had increased armor protection compared to other modern Yugoslav tanks. The front hull side was angled at 71° and the new armor construction was to provide protection the equivalent of 650 mm thick homogeneous steel plate armor according to M. C. Đorđević (Odbrana Magazine). Other sources, such as like www.srpskioklop.paluba, listed the frontal armor thickness to be equivalent to 500 mm of homogeneous steel armor. Against HEAT rounds, it offered 600 mm protection. The flat side armor plates were much weaker, with a thickness of just 70 mm.

The turret front armor thickness is unknown. What is known however is that it was angled at 40° and provided the same level of protection as the hull front armor. Similar to the improved M-84 versions, the Vihor also had a cast turret. In addition, its turret front had a cavity that was filled with quartz sand mixed with an adhesive.

Additional protection could be acquired by adding anti-HEAT screens or Explosive-Reactive Armor (ERA). In the case of the Explosive-Reactive Armor, it was a domestically developed KAO M-99 type. These, in the best case scenario, provided an 80% increase in protection against HEAT rounds. More realistically, these provided additional protection in the area of 30% to 50%. Against kinetic rounds, it offered a slight increase of protection of around 25%. The M-99 armor was immune to fire up to 23 mm caliber rounds, including artillery shrapnel or detonations of close positioned explosive-reactive units. This armor added a total weight of 750 kg, a further 250 kg if the sides were also protected. The development of this armor began in early 1990s, and it was not yet ready to be added on the prototype. It was actually never fully installed on any Vihor tank.

The Vihor was also to be equipped with the BDK smoke dischargers. These consisted of 24 discharge units, divided into two groups, and placed on either side of the turret. The maximum effective range of this system was 500 m. Besides standard smoke rounds, illumination, anti-infantry, or anti-missiles flares could be used.

The Vihor was also provided with Nuclear Biological Chemical (NBC) protection. It received an inner lining that protected the crew from neutron radiation. A detector for biological weapons was also added. Lastly, an automatic fire extinguisher system was installed inside the vehicle.

The last and probably one of its greatest assets was its small size. Generally speaking, all Soviet tank designs (which were copied by JNA) had smaller dimensions than Western designs, and the Vihor was no exception. Its total volume was around 12.6 m3.

Crew

The Vihor had a crew of three, consisting of the commander, the gunner, and the driver. Their positions were unchanged in comparison to the M-84 tanks. The gunner and the commander were placed in the turret, while the driver was positioned in the lower hull.

The Fate of the Project

The single pre-prototype was equipped with an M-84 turret and used for extensive drive testing. Depending on the sources, this vehicle managed to successfully drive between 1,500 to several thousand kilometers. No major problems with the first design were noted. While the development of the Vihor was underway, the Yugoslav wars broke out. This marked the end of many military projects, including the Vihor. The first pre-prototype test vehicle was located in Belgrade, nowadays Serbia, prior to the war. Due to a lack of documentation and proper equipment, it was not possible to fully finish this prototype. It would eventually be stored in the VTI Kumodraž depot. In 1993, a new Vihor project was announced, which was to have a stronger engine and hydrodynamic suspension unit. This project led nowhere and was likely just a propaganda tool to boost morale. At that time, Yugoslavia was under sanctions and in a dire economic situation, so developing such a design would have been almost impossible.

Two completed prototype hulls were located at the Đuro Đaković workshop, while the two incomplete turrets were left in Slovenia when the war started in Yugoslavia. The Croatians would use the two hulls together with the available documentation and tooling to start their own tank development project. This would lead to the creation of the Degman and M-84A4D projects, which are currently at the prototype stage.

Conclusion

The Vihor was the JNA’s final attempt to develop a modern domestic tank design. It would have possessed a series of advanced systems and, combined with good overall driving performance, held the promise of becoming an excellent design. Unfortunately, its final realization was stopped with the outbreak of the Yugoslav wars. How would it have performed in future testing and evaluation is difficult to know precisely. It was nevertheless an interesting design initiated when Yugoslavia was in a huge political and economical crisis, which ended in a war and the cancellation of this and many other projects.

Vihor M-91 specifications
Dimensions (L-W-H)	9.74 x 3.65 x 2.21 m
Total Weight, Battle Ready	44 tonnes
Crew	3 (driver, commander, and gunner)
Propulsion	1,200 hp​​  B-46-TK-1
Speed/off-road	75 km/h, 50 km/h
Range	600 to 700 km
Armament	125 mm 2A46, One 7.62 and one 12.7 machine gun.
Armor	Equivalent up to 500 to 650 of homogeneous armor
Number obuilt	At least three incomplete prototypes

 

Sources 

• M. C. Đorđević (2015), Odbrana Magazine
• M. Jandrić, Seventh Decade of the Military Technical Institute (1948. – 2013.)
• B. B. Dumitrijević (2010), Modernizacija i intervencija, Jugoslovenske oklopne jedinice 1945-2006, Institut za savremenu istoriju
• M. Dragojević (2003) Razvoj Našeg neoružanja VTI kao sudbina, Zadužbina Adrijević
• Magazine Poligon 2/2018
• https://www.vs.rs/sr_cyr/o-vojsci/naoruzanje/oklopne-jedinice
• http://www.srpskioklop.paluba.info/vihor/opis.html
• http://www.srpskioklop.paluba.info/m84/opis.htm
• VIHORog/reboot/whirlwind-mystery-yugoslavias-m-19-heavy-tank-188810