Throughout the history of warfare, rivers and lakes have impeded an army’s mobility. This is particularly problematic for tanks which are heavier than most military vehicles. When existing bridges capable of supporting tanks are destroyed or too heavily defended to be worth the risk of assaulting directly, alternative water crossing methods must be sought. The first option is to construct pontoon bridges, which risks mass casualties when spotted by hostile artillery observers. The second option is to operate tanks with underwater wading equipment: they travel on the riverbed with an extended snorkel tower for the commander to maintain observation. However, deep wading gear imposes extra costs on each unit. Installing temporary floats on tanks to swim constitute a third choice; the most famous examples were the Sherman ‘DD’ tanks of the Operation Overlord landings at Normandy. Swimming apparatus is difficult to design and is prone to failure though. Laying bridges, readying a snorkel equipped tank or installing swimming gear are all time consuming. A fourth way is to produce a tank that swims without onerous sealing procedures or add on equipment: the Soviet PT-76 is the most successful practitioner of this philosophy.
The PT-76 (Plavayushchiy Tank: floating tank) owes its existence to the Soviet Army’s desire for light tanks capable of reconnaissance ahead of slower medium and heavy tank formations; they also wanted to cross water obstacles to pursue a fleeing enemy without the delay of preparing deep fording equipment or waiting for engineers to build bridges. The Soviet Union had developed the T-37A and T-38 amphibious light tanks in the 1930s but their 3–9mm armour and single machine gun armament rendered them pitifully non-survivable during the Great Patriotic War. The Soviet wartime industry’s prioritization on medium tanks and assault guns like the T-34/76 and SU-76M forced a production cap of the marginally better armed T-40 to 222, favouring the non-amphibious T-60 and T-70. When the Germans retreated from the USSR in late 1943 onwards, the absence of amphibious vehicles sufficiently armed to harass them permitted the defeated invaders time to regroup and slow the Soviet advance westwards. The surrender of Nazi Germany and the dawn of the Cold War opened the possibility of conflict in Central Europe, which features water obstacles every 40–50 km.
Renewed interest in filling the capability gap left by obsolete and scarce amphibious wartime light tanks resulted in Order Number 3472 by the Soviet Council of Ministers in August 1949 for both a light tank and armoured personnel carrier that may traverse water bodies with minimal preparation. The VNII-100 (Vserossiyskiy Nauchno-Issledovatel’skiy Institut: All Union Scientific Research Institute) was the supervising authority for Obiekt 740, the leading prototype jointly developed at Leningrad Kirov and Cheylabinsk Kirov factories (LKZ and ChKZ — ‘Z’ for zavod, ‘plant’). Located east of the Ural Mountains, ChKZ was the outcome of ChTZ (T — Traktornyy: tractor) absorbing LKZ when it evacuated eastwards beyond German bombing range in World War 2. Following the Nazi capitulation, most of the design cohort returned to Leningrad but ChKZ retained the heavy assembly lines necessary for producing tanks.
Design parameters were a weight not exceeding 14 tons, armour protection of 10mm, a 76mm gun with 35–40 ready rounds, a maximum speed of 40 km/h and 10 km/h on land and water, respectively. The prototype’s designers were under an enormous amount of pressure to create a working prototype within a year; the failure of Krasnoye Sormovo (Shipbuilding Plant 112) to produce a functional carriage in 1948 had resulted in the firing and ‘bringing to justice’ of its directors on the orders of Stalin.
Creating a tank that could swim presented the contradictory need to be light and buoyant but rigid and strong enough to absorb travelling over rough ground, water pressure and waves along with recoil forces of the main gun and incoming fire. Obiekt 740’s frontal aspect featured a lower glacis plate raised well above the waterline to prevent it from ‘dolphining’ its nose downwards; a wave reflector on the upper glacis may be unfolded to divert water away from the driver’s hatch. A phenomenon to overcome was the displacement of the tracks from the roadwheels and drive sprocket after a water crossing; this occurs when the tracks running under the roadwheels sag and cause the track links running above them to go taut and lose engagement with the drive sprocket’s teeth. The Obiekt 740 obviated this problem with double guide teeth on the tracks running on the outsides of large diameter roadwheels and drive sprockets.
For water propulsion means, the LKZ and ChKZ team debated three types of screw propeller drives. However, water jets proposed by Nikolai Shashmurin were chosen mainly because impellers ensconced within tube channels and protected by grills were far less exposed to entanglement by reeds and damage from pebbles than boat style propellers. Shashmurin did not prevail in the gear box choice though; his proposed design was spurned in favour of one shared with the T-34 tank. While it made economic sense to use existing technology, the necessity of modifying it for compatibility with the water jets added 300 kg to its overall weight.
Only one other rival prototype challenged the Obiekt 740 for the evaluation trials, the K-90 designed in Moscow based VRZ No 2 (Vagonnaya Remontnaya Zavod — Wagon Repair Plant) by Colonel Anatoly Kravtsev. Created from parts sourced from the T-70 light tank and M2 artillery tractor and driven in water by propellers, the K-90 differed considerably from the Obiekt 740 in possessing high inclined side walls, a rear off set turret and return rollers above the roadwheels. Kravtsev’s candidate performed dismally in most of the tests, struggling to climb up a riverbank after getting hobbled by floodplain. The Leningrad — Chelyabinsk candidate overcame most of the same challenges with ease, resulting in the August 1952 approval for serial production by the Soviet Council of Ministers with the type classification of PT-76.
The Tank that Swam to Battle
Produced at Stalingrad Tractor Plant (STZ) rather than its birthplace ChKZ, PT-76s were assigned to special amphibious companies of tank and motorized rifle regiments. When the regiment came upon a river obstacle, the PT-76 company swam across first to secure the opposite bank while conventional tanks readied their deep fording gear or awaited the arrival of bridging equipment. PT-76s were additionally allocated to reconnaissance companies of Motor Rifle and Tank Regiments; a similar complement existed in the recon battalion of a Motor Rifle or Tank Division.
When the MP (Morskaya Pekhota: Naval Infantry) was revived as a subordinate arm of the Soviet Navy in 1963, their three regiments of the Northern, Baltic and Black Sea fleets fielded a mixed tank battalion of PT-76 and T-54/T-55 medium tanks. The PT-76s were intended as beach assault tanks to support the marine infantry battalions. The sole MP division of the Pacific fleet added a tank regiment of the same two vehicles in addition to the existing tank battalions within its organic infantry regiments.
Just five years into its production, the PT-76’s most significant change in 1957 was the replacement of the D-56T main gun, distinguished by a multi-slotted muzzle brake, with the D-56TM. The latter weapon mounted a bore evacuator sleeve on its barrel for keeping propellant gases out of the turret compartment and a simpler double baffle muzzle brake. To comply with the Soviet military’s move from single to double digit radio frequencies on armoured vehicles, the 1940s vintage 10RT-26E radio (3.75–6MHz) was swapped out for the R-113 Granat (20–22.375MHz).
Switching to the D-56TS with STP-2P Zarya two axis gun stabilizer, installing PAZ (Protivoatomnaya Zashchita: anti-nuclear protection) overpressure apparatus for sealing the habited sections from nuclear, chemical and biological contaminants and three flat external fuel tanks for increased driving range in 1959 culminated in the PT-76B.
Like almost all other Soviet armoured vehicles, it was inevitable that the PT-76’s body was manufactured into diverse offshoots. Developed simultaneously as its forbear and entering mass production in 1955, the BTR-50P (Obiekt 750) armoured personnel carrier ditched the turret for a cabin superstructure with capacity for 20 soldiers or two tonnes of cargo. In World War 2, Soviet infantry clung onto the hand rails of tanks because trucks were restricted to roads; the BTR-50P was a first step in the Army’s quest for permitting greater mobility for infantry under armour protection. A key quirk of this opened top APC was a winch to pull an 85mm D44 anti-tank gun or 107mm B11 recoilless rifle into its troop cabin after folding down a pair of loading ramps at the back. Bracing the gun’s outriggers against the BTR-50P’s rear corners turned the APC into a mobile direct fire artillery. For good measure, a GAZ-69 light truck in need of a river fording could piggy back the BTR-50P. From 1958 onwards, the BTR-50PK (krytkiy: covered) sacrificed the roll in gun capability for a roof with three egress hatches over the cabin; it was preferable to keep grenades and Molotov Cocktails out of the vehicle if it were to face down angry mobs in an urban setting like the Hungary uprising two years earlier.
Armament on the BTR-50P/PK was very modest: a single 7.62x54mm SGMB (PK or PKB from 1968) machine gun with a total of 1250 rounds was available for clipping to one of two pintle cradles in the troop compartment. Armament upgrades for a 14.5mm KPVT on the commander’s station (BTR-50PA) or ZPTU-2/4 multi barrel weapons to turn it into a mobile anti-aircraft carriage were tested but ultimately rejected. This did not prevent export users from concocting their own rigs; North Vietnam added 23mm cannons to most of their BTR-50P/PKs which saw action in the 1972 Easter Offensive against their Southern brethren.
The BTR-50P and PK were not wholly adequate as combat vehicles notwithstanding their aquatic mobility. Entry and exit through the roof was certainly awkward for embarked soldiers burdened with personal gear and fatal when performed under fire. The Soviet Motor Rifle infantry’s triadic organization of three nine man squads making a platoon created troop management chaos since the BTR-50P/PK carried the equivalent of a half platoon. Lastly, the possibility of nuclear contamination in war time necessitated a troop carrier with embrasures for the passengers to shoot from without leaving it. Following their displacement from the MR infantry formations by the BMP-1 infantry fighting vehicle, the BTR-50P family lingered on elsewhere in the Soviet Army as mobile command centres (BTR-50PN, BTR-50PU), mine clearance engineers (UR-67) and breakdown tractors (MTP-1).
While studies of the Cold War and nuclear disarmament are focused on strategic weapons that may be only authorized by state leaders to roast major population centres and military-industrial installations, ‘tactical nuclear weapons’ were intended for military leaders to do the same to frontline armies. Long range battlefield artillery rockets and missiles were a parallel development for delivering the new TNWs, high explosive or chemical payloads; these descendants of the wartime German V2 were intended against high value targets beyond the range of either tube artillery or multiple rocket launchers.
An early system was the 2K1 Mars, a nine meter long solid fuel unguided 3R1 rocket cradled on a 2P2 Transporter Erector Launcher (TEL) based on the PT-76 chassis. They were assigned to Motor Rifle or Tank Divisions while larger ‘Scuds’ (the NATO name for R-11 and R-17 short range ballistic missiles) were ‘operational’ Army and Front level assets. With only twenty five TELs produced and a modest maximum range of 17.5 km, Mars was quickly displaced by the 2K6 Luna a couple of years later. Their TELs were also built on the PT-76 but added two return rollers on each side.
Luna TELs did not operate alone; the Tank/Motor Rifle Division’s single SSM (surface to surface missile) battalion accorded a retinue of 2U663 or 2U663U semi trailers for transporting reloads, GAZ-69 light trucks for site surveying, K-51 cranes and warhead assembly shops embarked on ZiL-157 trucks to service its three launchers. They lingered on in Soviet service till 1982 and were exported to North Korea, East Germany, Cuba, Poland and Romania, but declined in favour of the 9K52 Luna-M (NATO: FROG-7) from 1964 onwards. Six Luna complexes were deployed to Cuba to oppose a possible American invasion to eliminate the Soviet R-12 and R-14 medium and intermediate range nuclear weapons that set off the Missile Crisis of October 1962.
Soviet VDV (airborne forces) in the Cold War are distinguished by their preponderance of air portable armoured vehicles compared to their lighter US counterparts. Their first assault gun, the ASU-57 (Aviadesantnaya Samokhodnaya Ustanovka: Airborne Assault Gun), was outclassed almost as soon as it entered service because its weapon was ineffectual against contemporary NATO tanks like the M48 Patton and Centurion. Designed by Nikolai Astrov at Mytishchi Machine-Building Plant (MMZ) and produced from 1959–1966, the succeeding ASU-85 sported a meatier 85mm D70 (2A15) tube and SGMT co-axial machine gun on the PT-76 chassis. It gave up its root vehicle’s water jets and buoyancy to meet air transportability size and weight restrictions. Since the Soviet high command anticipated that dozens of assets would be lost during a contested drop, the PT-76’s V6 engine was swapped out for a cheaper YaMZ-206V two stroke diesel powerplant derived from trucks. A Soviet Airborne Division was allocated a single assault gun battalion of 31 ASU-85s; 30 were split evenly into three companies and the last was the battalion commander’s mount.
PT-76’s Global Resume, Including the Birth of a Nation
The BMP-1 doomed the PT-76’s career in both reconnaissance subunits of Soviet Motor Rifle and Tank formations from 1966 onwards. Endearingly (or mockingly) named Poplavok or Plyvun (float; quicksand) by the troops, the PT-76 was not ideal as a scout vehicle notwithstanding its amphibious mobility. It was necessarily large to permit buoyancy, but far more difficult to conceal than the BRDM and BRDM-2 scout car. It was not terribly fast on land and lacked specialist observation or recording equipment for documenting discovered enemies from a safe distance. Its 76mm medium pressure gun was adequate for bunkers and exposed dismounts but outclassed against other tanks packing calibres of 90mm and above. The BMP-1 was just as amphibious and not significantly better protected but offered more flexibility in the reconnaissance role; its embarked six man scout squad offered more eyes and ears with hand held specialist tools than the PT-76’s three man crew. The possibility of a conventional war with NATO escalating into a nuclear conflict curtailed the possibility and need to rapidly force river crossings to invade Europe despite the Soviet Union’s post war desire to avoid fighting a war on its own soil ever again.
Details on the PT-76’s combat use in Soviet service are annoyingly limited to short mentions because the interventions they appeared in, like the 1956 and 1968 interventions in Hungary and Czechoslovakia were very brief. The PT-76 saw action in Chechnya after the Soviet Union’s dissolution with the Russian MVD (Interior Ministry) but histories of armoured warfare in those conflicts are more concerned with the ravages visited upon T-72 and T-80BV main battle tanks in Grozny.
Outside of Europe though, the Poplavok built a solid record of combat participation. Even though the North Vietnamese Army fought much of the Vietnam War with infantry and indirect fires, it did possess mixed armoured regiments of T-34/85, T-54 and PT-76 battalions. They too received Norinco Type 63s, a Chinese made four man crewed amphibian with the PT-76 hull and a dome turret packing a 85mm gun. When the US committed ground forces to aid South Vietnam against the North’s unification war in 1965, the latter preferred to hold back its armour in anticipation of a direct American invasion. The Ho Chi Minh trail was not suitable for supporting the movement of armoured vehicles at the beginning of US main force involvement. Even though the NVA prior to 1972 was the underdog in South Vietnam, losing thousands of soldiers to America artillery and aerial bombing, in neighbouring Laos it was the dominant conventional army. In January 1968 NVA PT-76s overran the Royal Lao Army outpost of Ban Houei Sane in Military Region 3, the upper panhandle of Laos. The NVA then rolled over the Neutralist faction’s Muong Soui base in June 1968 with ten PT-76s leading the way for infantry and sappers, the first time communist armour was used in Military Region 2 of that country’s northeast. Even though the Royal Lao Air Force and the US military’s control of the air often punished the PT-76s and other tanks severely, the NVA used Laos as a ‘laboratory’ for practicing armour tactics prior to their full scale conventional invasion of South Vietnam in March 1972.
US ground troops only confronted NVA PT-76s twice in South Vietnam. In January 1968 the Lang Vei Special Forces camp, located between the Laos — Vietnam border and Khe Sanh combat base, was crushed by a PT-76 company and attendant infantry assaulters. As a cruel irony, survivors of Ban Houei Sane’s fall had taken refuge in Lang Vei. The Americans got some payback against the Poplavok when ten stormed Ben Het Special Forces camp in March 1969 — the North Vietnamese were willing to risk their armour to stop the camp’s M107 guns dropping 175mm shells on their base camps. In the only battle between US operated and NVA tanks of the entire Vietnam War, a platoon of encamped M48A-3 Patton medium tanks destroyed two PT-76s and a BTR-50PK, forcing their retreat. The PT-76s got in their own licks though; a direct hit on one of the Pattons that was revealed by its muzzle flash killed two crewmen and wounded two others.
NVA PT-76s occasionally made local river crossings, but mostly battled in a very conventional manner on land. The NVA’s unfamiliarity with infantry and armour co-operation, the competence of ARVN tank gunners and American aerial dominance over South Vietnam mauled hundreds of PT-76s and Type 63s. However India’s intervention in the Liberation War for Bangladesh on the side of pro-independence movements against (West) Pakistani rule that the Poplavok operated in a country seemingly made for amphibians. Formerly named East Pakistan, the South Asian country owed its well irrigated and fertile soil to dozens of rivers and wetlands along with low elevation above sea level. With little chance of reinforcement from the West, which was separated by over one million square miles of Indian territory, the strategy of Pakistani forces in the East was to bleed the numerically superior Indians by fighting from fortified garrisons. To overcome the defenders, Indian PT-76s made frequent use of their aquatic mobility for both tactical and operational manoeuvres (short distance movements during combat engagements and long distance positioning of large formations within a theatre of operations, respectively). Twelve soldiers could hitch a ride on each of these tanks, permitting close armour — infantry cooperation. Several weaknesses in Pakistan’s army in the East gave India’s Poplavok an operational permissiveness not enjoyed by their North Vietnamese counterparts: the scarcity of air power (just one Pakistani F-86F squadron); the relative obsolescence of their M24 Chaffees whose gun barrels were too worn to permit any accuracy beyond 1000 m and inconsistent use of infantry operated anti-tank weapons.
Waning Days of the Wading Tank
Production of the PT-76 ended in 1967 with nearly 12000 units completed. In the same year, a final round of modernization was implemented for new units or existing ones turned in for capital rebuilding: replacing the SGMT co-axial machine gun with the Kalashnikov designed PKT, the R-113 radio with the R-123 Magnoliya, R-120 internal communications with the R-124 and headlight updates.
The modern Russian Naval Infantry has held on to the PT-76 decades after the Ground Forces dispensed with them. A modernized PT-76M (Obiekt 740M) with a faceted hull, 300 hp V-6M powerplant and extra fuel tank for increased range was designed in 1960 at STZ but was not accepted for mass production. A long overdue replacement, the BMP-3F, is a navalized modification of the original BMP-3 IFV with periscopic air intake extension, trim vanes added around the turret and increased buoyancy: these changes grant it a continuous floating endurance of seven hours.
Foreign users of the Poplavok have performed their own customizations. Abandoned Egyptian PT-76s seized by the Israelis as war booty in 1967 were given US radios and MAG machine guns to facilitate logistical and communications compatibility; they were promptly turned against their former owners in the 1973 Yom Kippur War. The gigantic archipelago nation of Indonesia has extended the lifespan of its seventy strong PT-76 fleet by installing the Belgian designed 90mm Cockerill Mk 3M-42 gun and its associated fire control system; the new weapon’s autoloader significantly reduces the workload on the tank commander who doubled as the loader for the original D-56T series gun. Together with a 300 hp Detroit Diesel 6V-92T powerplant and renewed utilities (electrical and cooling), they have been colloquially called ‘PT-2000s’.
The retirement of the PT-76 from Russian service has not posed any barrier to that country’s arms industry offering longevity upgrades to overseas customers. OJSC (Open Joint Stock Company) Muromteplovoz’s Soviet legacy vehicle program proffers a 15 year lifetime extension to the Poplavok with a 300 hp YaMZ-7601 powerplant for a 50% speed increase and a multi weapon turret packing a 30mm 2A42 cannon, 30mm AG-17 automatic grenade launcher and PKTM coaxial machine gun. Burevestnik Central Research Institute’s AU-220M Baikal turret is a more threatening option: it houses a 57mm BM-57 automatic cannon that shares the same ammunition as the S60 anti aircraft gun. While these armament options are more versatile than the original, it remains to be seen if they will attract widespread interest.