Light Amphibious Tank Project – Lek Plavasht Tank ‘Oktopod’

People’s Republic of Bulgaria (1988-1990)
Light Amphibious Tank – Small Scale Mock-up Only

While thinking of tank-building countries, Bulgaria is unlikely to be amongst the first dozen to come into one’s head. Just like other Warsaw Treaty Organization (WTO) countries (composed of the Soviet Union, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, and Romania), which usually used imported Soviet vehicles and, at best, proposed modifications for those, Bulgaria is not rich in unique projects. However, one such project, born at the dawn of the existence of Socialist Bulgaria, is known. This was a project for a light amphibious tank based on the Bulgarian BMP-23 IFV.

History of the Project

Soviet ‘Great Grandpa’ and ‘Grandpa’

The history of the Oktopod goes back to the beginning of the 1960s, when the Soviet ‘MT-LB’ APC, or, during development, ‘Object 6’, was adopted by the Red Army. One of the most recognisable and mass-produced lightly armored vehicles of the Cold War period, along with the American M113, it was also used as a base for dozens of not only Soviet, but also Belorussian, Kazakhstani, Polish, Russian, Ukrainian, and even Swedish concepts, prototypes and serial modifications. Bulgaria was another country that has been using this vehicle for more than half of a century.

A Soviet project of self-propelled howitzer named 2S1 was being developed after 1967. The main point was to create a modern 122 mm SPG which would be on par with its analogues from NATO. In 1970, it was adopted by the Red Army and named 2S1 ‘Gvozdika’ (Russian for Carnation). This was the first Soviet flower-named artillery piece, followed later by 2S2 ‘Fialka’ (Russian for Violet), 2S3 ‘Akatsiya’ (Russian for Acacia), 2S4 ‘Tulpan’ (Russian for Tulip), 2S5 ‘Giatsint’ (Russian for Hyacinth), 2S7 ‘Pion’ (Russian for Peony), 2S8 ‘Astra’ (Russian for Aster), and 2B9 ‘Vasilek’ (Russian for Cornflower). Gvozdika became another iconic vehicle of the Soviet army, with more than 10,000 examples produced. It was exported to literally half of the world, and was used as a base for many projects. Amongst those projects was the Bulgarian BMP-23 IFV.

Son of an Immigrant

The BMP-23 was developed in the 1980s. It was a vehicle tailored to the needs of the Bulgarian Army, then under the Soviet sphere of influence as part of the Warsaw Pact. The overall goal was to have an improved IFV compared to the BMP-1 already in service. The vehicles were first shown on a military parade in 1984. Given the goals of the military, it had to be given sturdier armor than that of the BMP-1. The better engine and reinforced suspension of the 2S1 helped in this way. The hull was also comprehensively modified to integrate a roomy troop compartment at the rear for six fully-equipped infantrymen seated back-to-back. The rear was modified to accept two doors for dismounting, in addition to the two large roof hatches. Three pistol ports were also placed in the sides of the hull, all of which were fitted with bulletproof vision devices.

Development of the ‘Oktopod’

At the end of the 1980s, Bulgarian engineers were working on a concept of light amphibious tank based on the BMB-23 Infantry Fighting Vehicle. The vehicle was meant to be used in the Balkan mountains. The main potential opponents were Greece and Turkey, both members of NATO. At the time, the Bulgarians thought these countries were going to buy Leopard 2 main battle tanks. The assessments of the new tank’s firepower were based on the T-72 tanks Bulgaria had and also on the Yugoslavian M-84. The new light tank was suggested not only for the Bulgarian army, but also for exporting. By the end of 1988, the preliminary project was ready and was being reviewed at the highest state level.

Amongst the specialist team there were both Bulgarian and Soviet experts, which judged the project very highly. Despite this, the Soviets offered to supply PT-76 light tanks at a very low price, as well as assistance in their modernization. The offer was rejected, as these Soviet tanks did not meet Bulgarian requirements. The armor was too poor, and the 76 mm D-56 gun was too outdated and could not be used to fight against modern vehicles. The Soviets had to give in, and the development of the tank was continued. Work on producing a mock-up of the vehicle began, and soon it was planned to produce its first prototypes. Trials were planned.

Meanwhile, after 10th November 1989, a process of fundamental political reformation had begun in Bulgaria. The end result, beside the dissolution of the Eastern Bloc and the fall of Bulgarian communism, was that the amount of funding for the project declined rapidly. At this time, development was still in full swing, with negotiations being held with Sweden and Israel regarding the supply of modern turbo-diesel engines and observation devices for the tank.
Everything changed in the beginning of the 1990s, when funding was stopped, and the development team was dismissed. The project was abandoned, and most of the documents about the light tank vanished. Some sources claim they were deliberately destroyed. However, there is a chance they are still yet to be discovered. The only thing that has somehow survived through all this was the mock-up of the vehicle.

Name of the Project

The exact name of the vehicle is unknown. Hence, descriptive terms are usually used to distinguish it, such as ‘Light Amphibious Tank’ in English or ‘Лек Плаващ Танк’ in Bulgarian.

Some sources also relate the name ‘Oktopod’ (Bulgarian for ‘octopus’) to this vehicle. However, this is highly likely a contemporary term based on project’s similarity with Russian 2S25 ‘Sprut SD’ light self-propelled tank destroyer, although some sources claim this was the original name of the vehicle.
For convenience and better recognition, from now on, the vehicle will be referred to as ‘LPT Oktopod’ or simply ‘Oktopod’ in this article.

Description of the Vehicle

Hull and Turret

The hull of the ‘Oktopod’ was based on BMP-23 (which, in its turn, was based on the Soviet 2S1 Gvozdika self-propelled howitzer). It was shortened, with one row of road wheels removed and two rows of return rollers added. Clearance was increased.
Like the BMP-23, the vehicle was also supposed to be amphibious; hence, some aspects of its design were improved for better buoyancy – for example, the height of sides was increased. Swimming was supposed to be carried out by moving the tracks.
The turret of the vehicle was made in the form of a truncated cone, with two crew hatches on the roof. The estimated ring diameter was ~2.3 m. Installation of smoke grenade launchers was also planned.

Armament

The new light tank was supposed to be armed with the Soviet MT-12 ‘Rapira’ (Russian for Rapier) 100 mm anti-tank gun as its main armament, with a coaxial 7.62 mm PKT machine gun. According to some sources, a 14.5 mm KPVT was also planned (probably as an anti-infantry machine gun installed near the commander’s hatch).

100 mm MT-12 ‘Rapira’	APDSFS			HEATFS
	3BM1	3BM2	3BM24 ‘Kalach’	3BK3	3BK8
	3.38 kg		3.63 kg	10.072 kg	9.5 kg
	1,575 m/s		1,548 m/s	975 m/s	1,075 m/s
	–	–	–	0.84 kg charge (1.29 kg TNT equiv.)	1 kg charge (1.54 kg TNT equiv.)
	300 mm pen	235 mm pen	352 mm pen	350 mm pen	400 mm pen
	8-10 rpm	Parameters of penetration are given for 0 m and 0°.

100 mm MT-12 ‘Rapira’ gun parameters. Source: ZA DB, Pablo Escobar’s gun table

The MT-12 (2A29) Rapira was a smoothbore anti-tank gun developed in the Soviet Union, based on the T-12 (2A19) cannon. It was adopted by the Soviet army and entered mass production in 1970. The gun was designed primarily for direct fire, but it could also be used as an ordinary field gun for firing high-explosive ammunition from closed positions. The MT-12 took part in many conflicts, such as the Soviet–Afghan War (1979–1989), Transnistrian conflict (1989-1992), and Chechen Campaigns (1994-1996). Recently, the gun has been used in the Syrian Civil War and the 2022 conflict in Ukraine.

7.62 mm PKT	AP
	LPS
	3.38 kg
	855 m/s
	12 mm pen
	750 rpm (250 shots clip)

7.62 mm PKT machine gun parameters. Source: ZA DB, Pablo Escobar’s gun table

The 7.62 mm PKT machine gun was a tank version of Kalashnikov’s machine gun (Russian: ‘Пулемёт Калашникова‘). It was equipped with an electric trigger. The barrel was made longer and with thicker sides. This allowed more sustained fire and also required replacing the barrel less often. The PKT was installed on many Soviet and Russian tanks, APCs and IFVs, like the BMP-1, MT-LB, BTR-60, BRDM-2, and others. It was exported, produced and used by several dozens of countries, including China, Cuba, Czechoslovakia, DPRK, Finland, Poland, Romania, Serbia, Ukraine, Yugoslavia, and many others.

14.5 mm KPVT	AP
	B31	BS41
	0.06344 kg	0.06441 kg
	976 m/s
	37 mm pen	45 mm pen
	600 rpm

14.5 mm KPVT machine gun specifications. Source: ZA DB, Pablo Escobar’s gun table

The 14.5 mm KPVT (Russian: Крупнокалиберный Пулемёт Владимирова, English: Vladimirov’s heavy machine gun) was developed in 1944 and adopted in 1949. It combined the rate of fire of a heavy machine gun with the armor-piercing capabilities of anti-tank rifles. It was designed to combat lightly armored targets and manpower of the enemy located behind light cover, as well as to be an anti-aircraft machine gun. It was one of the most powerful machine guns ever used by the Soviet and later Russian armed forces. The KPVT used a 50-round belt.

It was planned to equip the 100 mm gun with an autoloader. The estimated elevation arc of the main armament was -6/+24o. It is worth mentioning that there is no data about any plans on equipping the vehicle with night-vision devices or thermal imagers. If there were no such plans, it would have been a serious drawback of the vehicle at that time.

Armor

The mass of the new vehicle was had to be less than 18 tonnes. Still, the vehicle had to be quite well-protected in comparison with its analogues. An innovative aspect of Oktopod’s armor was its multilayer structure.
The plates of rolled homogeneous steel armor were combined with plates of zeolite and stealth-armor.

Zeolite is a mineral used as an anticumulative filler. It is refractory and difficult to compress, which makes it a good protection feature for armored vehicles. According to some sources, the Bulgarians tested this technology on turrets of T-54/55 medium tanks. The external armor layer was to have radio-absorbing functions, provided by special materials and the absence of a gap between the sheets.

For sufficient mobility, it was planned to use a 500-700 horsepower diesel engine. At first, the designers wanted to use the engine of the T-55 or T-72. However, an opportunity of buying cheap and compact-sized Swedish turbo-diesel engines appeared. The engineers decided to seize it, so negotiations began. It was planned to organize the production of their licensed copies in the ‘Vasil Kolarov’ plant in Varna.
Although there is no data about the particular engine, it was highly likely to be Scania DS14 V8 turbo diesel engine, which could produce about 500-550 hp.

The DS14 was released in 1969 and was presented by Scania Trucks company as one of the most powerful truck engines of its time. It could raise power up to 350 hp – while average truck engine power of that time was almost 1.5 times less. Its construction (8 cylinders set in V-shape and divided into two equal groups, with piston groups forming a 90º angle) was beneficial in another aspect: its compact size, which made it possible to put the engine under the truck’s cabin. Since its release, DS14 was constantly being improved, and by the end of the 1980s, it already could outpet more than 500 hp in the version for the Scania R143 Streamline truck series.

Crew

The crew of the vehicle would have consisted of three men: commander, driver and gunner. The driver’s place was in the front-right part of the hull, next to the engine. The other two tankmen were to sit in the turret, to the left and to the right of the gun.

Israeli Observation Devices

It was planned to equip the vehicle with Israeli observation devices (periscopes), and negotiations for this took place. The exact model Bulgarians wanted to buy is not specified and currently unknown.

The Israeli main battle tank, the Merkava, developed at the end of 1970s, was equipped with an ‘Oranit’ ballistic computer. The driver’s periscope was equipped with a ‘Vilon’ night-vision device, the operation of which required the presence of infrared (IR) lights in the front of the vehicle. The commander and gunner could not see outside at night unless using a Star Light Scope (SLS) binocular or external illumination by spotlights. Later, the ‘Vilonʼ was replaced with the ‘Radian’, an Israeli copy of the American AN/VSS-2 periscope, working on SLS technology. It did not require IR lights to function any more.

The AN/VSS-2, or more precisely, its Israeli ‘Radian’ variant, is the most probable candidate to have been bought for Oktopod.

Possible Modernization

The concept of a light armored vehicle based on the MT-LB/2S1/BMP-23 has reappeared during a recent Bulgarian exhibition organized by Terem-Khan-Krum LLC (bulg. ‘Терем-Хан Крум ЕО­ОД’) – a Bulgarian company, specializing in the production, overhaul and upgrade of armored military vehicles. The exhibition was a part of the European Night of Museums event by UNESCO.
During the exhibition, a model was shown, which is similar to the known LPT ‘Oktopod’ mock-up in many aspects. First, the suspension and chassis are based on BMP-23’s. Second, the layout, as the model has a rear-mounted turret and a front-mounted engine compartment. Finally, the gun has aspect and proportions similar to those of MT-12 ‘Rapira’ ones.
On the other hand, there are some differences. The turret of the mock-up has significantly sloped armor plates, which probably indicates that it is cast (unlike the turret of the original mock-up, which is definitely welded). Sides of the rear part of the hull are made of two armor plates (one sloped plus one vertical). In addition, the general appearance of the described mock-up has significantly more details – as compared to the original one.
Nevertheless, it is important to remember that mock-ups often do not represent all details, as their main aim is usually to show general layout and the most important elements of the vehicles. Plus, the represented mock-up may be not the better detailed or modernized version of the LPT ‘Oktopod’, but a completely different unrelated project.

Conclusion

The project of Bulgarian Light Amphibious Tank was one of the most interesting vehicles designed in one of the Warsaw Treaty countries at the far edge of its existence. If built, it could have become the first serious AFV project developed in Bulgaria. Moreover, a mixture of different technologies (from the USSR, Israel, and Sweden) meant to be used to construct it would have significantly distinguished it from its analogues.
It is possible that in future, with further exploration of East European (mainly former WP) countries’ archives and private collections, which are tremendously lacking research now, more precious information (pictures, documents, blueprints, mock-ups, etc.) may be found. Thus, data about known vehicles (including LPT ‘Oktopod’) will be refined and clarified, and even new proposals may be unveiled.

LPT ‘Oktopod’(*) specifications table
Dimensions (L-W-H)	7.3 (8.8 with the gun) x 3.43 x 2.8 m
Ground clearance	0.43 m
Weight	18 tonnes
Engine	Scania DS-14 (~550 hp)
Suspension	torsion bar
Power-to-weight ratio (in hp/ton)	30.5 hp/ton
Maximum speed (ground/water)	60/4.5 km/h
Crew	3 (Commander, Driver, Gunner)
Driver vision’s devices	SLS-Vision ‘Radian’ or AN/VVS-2
Main Armament	100 mm MT-12 ‘Rapira’ with autoloader
Secondary Armament	7.62 mm PKT and 14.5 mm KPVT
Production numbers	0 built, mock-up only
(*) – vehicle’s original name is unknown; LPT ‘Oktopod’ is a speculative one.

Sources

https://www.vitalykuzmin.net/;
https://www.armedconflicts.com/The-nameless-project-of-a-Bulgarian-mountain-tank-t239318;
https://offroad-bulgaria.com/forum/основни-форуми/оръжие-бойни-действия-тактика-и-стратегия/оръдия-тежко-въоръжение/112321-бмп-23-1300-прашясаха-ли-вече/page2;
https://en.topwar.ru/143744-bolgarskiy-sprut-legkiy-plavayuschiy-tank-kotoryy-ubila-demokratiya.html;
http://www.gruzovikpress.ru/article/24532-yubiley-dvigatelya-scania-v8-ds-14-neveroyatno-realniy-motor/;
https://epicenter.bg/article/Shtyahme-da-proizvezhdame-balgarski-tankove/76768/2/0;
https://it.dir.bg/tehnologii/kak-balgariya-be-na-krachka-ot-sazdavaneto-na-sobstven-tank;
https://www.primeportal.net/tanks/david_lueck/merkava_mk1/index.php;
http://znametrg.com/2018/06/12/отзвук-от-една-изложба/;