Now the final part.
The PT-76B tank was a modernized version of the PT-76. It was developed at the design bureau of the STZ under the leadership of S.A. Fedorov and was adopted by the Soviet Army through the decree of the Council of Ministers of the USSR No. 1372-633 dated December 10, 1957 (and the order of the Minister of Defense of the USSR No. 13 dated January 10, 1958). During development, the tank carried the factory designation “Object 740B(Объект 740Б),” with V.I. Devchenko as its chief designer. Serial production was organized at STZ (later Volgograd Tractor Plant, VgTZ) from 1959 to 1967. By the end of 1965, the plant had modernized 912 older PT-76s, and over the entire production period, a total of 1,143 were manufactured.
Starting in 1960 and continuing until the end of serial production, significant design changes were introduced into the PT‑76B tank, which improved its combat and technical characteristics.
The differences of the PT-76 Mod. 1955(modernized in 1958~1964) and PT-76B Model 1962.
PT-76B Mod. 1959
The PT‑76B tanks produced in the first year were mainly distinguished from the original PT‑76 by the installation of a 76.2mm D‑56TS tank gun equipped with the two‑plane stabilizer STP‑2P “Zarya”(СТП-2П ‘Заря’). They also incorporated all of the modernization improvements that had been introduced into the PT‑76 design up to 1958.
(note- STP-2P stabilizer was also used in T-54B and T-55 tanks. but PT-76 Stabilizer system is much smaller.)
The STP‑2P “Zarya” stabilizer, with a dependent sighting line, was equipped with an electro‑hydraulic drive for the gun, an electric motor drive for the turret, and gyroscopic control units. It allowed the gun and its coaxial machine gun to remain automatically fixed in the chosen (stabilized) position in both vertical and horizontal planes while the tank was moving, and provided smooth regulation of aiming speeds.
Turret rotation in the horizontal plane could be carried out in both stabilized and semi‑automatic (non‑stabilized) modes. Control of the gun and turret, when the stabilizer was engaged, was performed from a control panel mounted on the gun’s elevation mechanism.
For aiming the gun and coaxial machine gun, The telescopic articulated sight TShK‑2‑66 was used. Previously, the TShK‑66 and TShK-66P(Mod. 1957) had been used. The gun’s elevation and depression angles ranged from −4° to +30°. The gun’s electric trigger button was located on the right handle of the control panel, while the coaxial machine gun’s trigger was on the left.
Reticle of TShK-66 Sight. fun fact, The PT-76 could fire different types of ammunition, such as HEAT and HVAP. However, the sight only had reticle for APHE, HE-Frag, and the coaxial machine gun. This was the same for all TShK-66 series.
The rate of fire of the D‑56TS gun reached 10 rounds per minute, with an effective aimed rate of fire of 7 rounds per minute. The ammunition load for the gun and its coaxial machine gun, as well as the stowage of crew weapons, hand grenades, and the signal pistol with its ammunition, remained unchanged compared to the PT‑76 model produced in 1958.
However, due to the tank equipped with a stabilizer, and because of changes in the layout of the fighting compartment (to accommodate stabilizer components), the rigidity of the 14‑round ammunition rack was increased and the method of securing the rounds was modified. In addition, the F1 hand grenade box mount was relocated from the right side of the turret to the 14‑round ammunition rack.
When the stabilized gun was installed in the tank’s turret, two lower and one upper stops with rubber shock absorbers were added to its armored mantlet and frame. As a result, the design of the mantlet’s protective cover was modified.
Because of the installation of an auxiliary hydraulic drive tank for the stabilizer in the front‑right section of the turret, the mounting of the rotating headlight was relocated from the turret roof to its right side.
With the installation of the main gun stabilizer, several additional changes were introduced into the PT‑76B’s design:
- The head light that was mounted on top of the turret was relocated to the side
- A protective guard for the gun on the commander’s side, and a contact block linked to the driver’s hatch handle.(If the driver’s hatch were open or locked, the turret can not be traversed.)
- A newly designed turret rotation mechanism with a backlash‑eliminating device; as a result, the toothed ring of the lower turret race was made 25 mm higher than on the original PT‑76.
- A contact block in the turret lock to break the power circuit when the turret was secured, and in the elevation mechanism a disengaging device that disconnected the cylindrical gear from the worm wheel when switching to stabilized gun‑laying mode.
- Reinforced sealing of the turret ring to improve watertightness during amphibious operations.
- A more advanced night‑vision device for the driver, the TVN‑2B.
To improve watertightness when afloat, the external sealing of the turret ring was enhanced by adding an extra felt gasket placed between the ring and the rubber seal. The external seal was arranged in the same way as the turret support seal of the T‑55 tank, differing only by the presence of a cut‑off contact linked to the tightening handle. This contact automatically switched off the turret‑rotation electric drive when the seal was tightened.
Starting in October 1959, the vehicle was fitted with a wave‑deflector shield widened by 50 mm.
The overall layout and placement of the main equipment inside the tank’s compartments (excluding the stabilizer units) remained unchanged. In the fighting compartment, several improvements were introduced for crew comfort and efficiency:
- The commander’s seat received an adjustable backrest and footrests mounted on the rotating floor, making it easier for him to operate during firing.
- For the loader, an additional handrail was installed to provide better support when working in a standing position while the tank was moving.
To prevent the commander’s periscope (TPKU) from being damaged by the gun’s recoil, the rotation of the commander’s cupola was restricted. Starting in September 1959, the TPKU sight was replaced with the upgraded TPKU‑2.
The tank was equipped with PPO(fire extinguishing equipment) and TDA(smoke‑screen device) systems, identical to those used on the PT‑76 model of 1958. Beginning in July 1959, a single handheld carbon‑dioxide fire extinguisher (OU‑2) was introduced for extinguishing fires in the driver’s compartment, the fighting compartment, and outside the tank. It was located in the driver’s compartment.
In the engine‑transmission compartment of the tank, a V‑6G diesel engine was installed, producing 176 kW (240 hp) at a crankshaft speed of 1,800 rpm. In all other respects—the power plant, transmission, running gear, and the vehicle’s external and internal communication systems—no significant changes were made compared to the PT‑76 model produced in 1958.
In the electrical system, due to the increased overall power demand of consumers (resulting from the use of the weapon stabilizer), a G‑74 generator with a capacity of 3 kW was employed, operating together with the RRT‑31M relay‑regulator. In the external lighting system, an FG‑102 head light with blackout device was installed.
The buoyancy reserve of the PT‑76B tank was 26% (3.6 m³ of displacement volume). Its speed afloat was 10 km/h, and in reverse 3–5 km/h. The turning radius was 12 m, with a 180° turn taking 20 seconds. The maximum towing force at mooring reached 13.7 kN (1,400 kgf).
PT-76B Mod. 1960
Starting in 1960 and continuing until the end of serial production, significant design changes were introduced into the PT‑76B tank, improving its combat and technical characteristics:
In January, to increase stern trim when moving afloat, the stowage of towing cables was modified. At the same time, the capacity of the bilge‑pumping equipment was increased to 460 liters per minute, and the manual bilge pump was replaced with an electrically driven pump.
In May, to facilitate fuel refueling, a more efficient refueling pump (MZA‑3) was introduced, which could be connected only to the driver’s socket.
In November, the V‑6PG engine with a crankcase heater began to be installed.
PT-76B Mod. 1961
In June 1961, an external activation point for the bilge pump’s electric motor was installed, allowing it to be switched on from outside when towing a disabled vehicle afloat. A 1.5‑meter cable with a push‑button switch was stowed inside a sealed box located on the hull roof, in front of the cooling system ejector on the left side.
From the end of the same year, the PAZ* system was introduced, providing protection for the crew and internal equipment against shock waves and radioactive dust when operating in contaminated areas. This was achieved by sealing the crew compartments, filtering incoming air from dust, and creating an overpressure of at least 0.15 kPa (0.0015 kg/cm²) using a centrifugal blower.
* PAZ(ПАЗ)= Противоатомная защита. It means Anti-nuclear protection system.
The PAZ system included: seals permanently installed on the tank; closing mechanisms that ensured automatic sealing; an engine‑shutdown mechanism (MOD); and a mechanism for automatic turret locking. Permanent seals were mounted on the gun, the coaxial machine gun, and the sight aperture.
The seals that closed automatically in the event of a nuclear explosion included: the cover of the turret ventilator window, the blower valve, and the cover of the hatch for the engine’s individual air intake.
Activation of the PAZ mechanisms was carried out automatically by the RBZ‑1M gamma sensor. The RBZ‑1M radiometric protection unit served as the detector for the entire PAZ system and was designed to send a signal to trigger the sealing devices, the engine‑shutdown mechanism (MOD), and the automatic turret lock in the event of a nuclear explosion—before the shock wave reached the tank. It also switched off the electric motors of the ventilator and blower (if they were running).
The device was powered from the vehicle’s onboard DC electrical system at 24–29 volts. The RBZ‑1M was mounted to the left of the commander, on the turret wall.
With the introduction of the PAZ system, the manual travel lock for the turret was replaced by a double‑action toothed turret lock. It was designed both for automatic locking (triggered by a pyrotechnic cartridge) to prevent turret rotation at the moment of a nuclear explosion, and for manual locking during travel. In addition, a new design was introduced to keep water and dust out of the TShK‑66 sight, which used K‑108 optical glass.
To improve the driver’s ability to monitor the control and dashboard instruments, to make it easier to manage the electrical circuits, and to provide more reliable protection against overloads and short circuits, a new central panel for the driver was installed. Onto this panel were relocated the switches for the TDA, the GPK-49 gyro semi‑compass, and the electric bilge pump.
Above. pre-1961 dashboard, below is the new version of dashboard.
The design of the turret’s distribution panel was also modified, with circuit breakers introduced to protect the electrical network.
the side towing hooks were replaced with smaller, lighter hooks mounted horizontally. This change made it easier to towing a disabled other vehicle while it was afloating.
PT-76B Mod. 1962
A picture of PT-76 Mod, 1962. This is a post-1964 upgrade, as it is fitted with T-54/55 fuel tanks.
January. In the air‑cleaning system, a two‑stage combined‑type air cleaner called VTI‑10. with ejector dust removal from the dust collector was introduced. To increase vacuum and improve dust extraction in the ejector, the exhaust from the third and fourth engine cylinders was combined using a manifold, and a special high‑pressure ejector was installed.
[Translator’s Commentary = the ejector acted like a vacuum cleaner powered by exhaust gases, helping keep the engine’s air intake clean even in dusty environments.]
In connection with the introduction of the new air cleaner, the rigidity of the engine bulkhead was increased by adding corrugations (from February).
To monitor engine operation, an hour meter (ChP‑563) was introduced, which was mounted on the left fender behind the cover of the left hatch inside the engine‑transmission compartment. In addition, starting in April, a speedometer was relocated to the right of the driver.
To reduce the weight of the vehicle, the armor thickness of the upper glacis plate of the hull was decreased from 10 mm to 8 mm (from May)
The fuel capacity of the engine’s fuel system was increased to 390L by installing an additional 140L fuel tank in the engine‑transmission compartment behind the gearbox and by modifying the overall connection scheme of the internal fuel tanks to the fuel distribution valve (from September). As a result, the tank’s operational range increased to 370 km on roads and 120 km afloat.
To improve the tank’s navigability in water, a hull of greater displacement was introduced by increasing its height by 70 mm and changing the angle of the lower glacis plate from 45° to 55° relative to the vertical (from October). To allow water to drain more easily from the rear part of the hull roof, a slight reverse slope was added. The vehicle’s buoyancy reserve increased to 28% (3.9 m³).
November. For operating the tank in marine conditions, a special flange was welded to the turret at the ventilator fan to allow the installation of an air intake pipe; the supply of these pipes was carried out only by special order of the Soviet Navy.
Air intake pipe or snorkel was attached in back of the turret.
An azimuth indicator was installed on the housing of the turret rotation mechanism, which was used to measure the angles of turret rotation relative to the hull of the vehicle, as well as the horizontal aiming angles when firing from covered positions (from December).
PT-76B Mod. 1963
Starting in May, the tank’s suspension system was upgraded to improve reliability. Engineers introduced “captive torsion bars,” which meant that the torsion bars on the right side could no longer be swapped with those on the left side.
Additionally, a safety feature was added to the turret system. When the turret is locked, a special switch (block contact) automatically cuts off the power to the electric drive. On top of that, the turret is designed to lock itself automatically whenever the PAZ safety system is triggered.
In August, to ensure that the tank’s turret could be securely locked in the rear-facing position during railway transport, an external turret locking device was introduced.
At the same time, to reduce the complexity and labor required in manufacturing, the fuel system’s pipeline connections were simplified: the previous coupling-type joints were replaced with hose connections.
PT-76B Mod. 1964
Starting in January, to reduce the time needed to warm up the engine in cold outdoor temperatures, a newly designed heater began to be used. This heater had higher heat output and came with a standardized blower and a unified control panel.
In February, the bullet resistance of the viewing devices was increased by replacing the cast frames with welded ones that had thicker walls (up to 10 mm on the sides and up to 15 mm at the rear).
At the same time, to reduce manufacturing effort and the overall weight of the tank, the travel-position turret lock (which fixed the gun either forward or backward) was eliminated, since the automatic locking system of the PAZ already provided both automatic and manual turret locking in any position.
Starting in May, on the roof of the engine-transmission compartment (MTO), the T-34 cylindrical auxiliary fuel tanks were replaced with two flat auxiliary tanks (taken from the T-54/55), each with a capacity of 95 liters. These tanks were not connected to the engine’s fuel system.
T-54/55 fuel tanks
In addition, the vehicle’s spare parts kit (ZIP) included one identical flat tank for low-freezing liquid, replacing the two round containers previously supplied for oil and antifreeze.
In September, lubrication of the spherical bearings in the side clutches was improved by adding an extra lubrication point.
Starting in October, to enable the vehicle to maintain a set course for longer periods with greater accuracy during swimming and when operating under difficult navigation conditions, the gyro semi-compass GPK‑48 was replaced with the GPK‑59(ГПК-59).
GPK-59 gyro compass
Starting in November, the tank was equipped with the V‑6B engine together with a G‑6.5 generator rated at 6.5 kW and an R‑10T relay regulator.
At the same time, to improve the grouping and accuracy of fire from the SGMT machine gun, a compensator spring was added beneath the rear slide of its mount. In addition, to ensure more thorough cleaning of the oil in the engine’s lubrication system, an MTs‑1 filter was introduced
In December, to improve the design and reduce weight, the headlights FG‑100, 101, 102 were replaced with the newer FG‑125, FG‑126, and FG‑127 models.
PT-76B Mod. 1965
For the sake of standardization, the previous fire‑extinguishing system (PPO), which included a KP‑50 automatic unit and four thermal fuses, was replaced with a unified PPO system (UA PPO). This new system consisted of an AS‑2 automatic unit, a KRR‑2 relay distribution box, four TD‑1 thermal sensors in the engine‑transmission compartment (MTO), and two KUV‑3 fan control boxes.
Starting in January, fire suppression was carried out using two carbon dioxide cylinders, each with a capacity of 5 liters.
Starting in March, the driver’s control panel was equipped with illumination provided by two KLST‑64 lamps.
Starting in April, to clean the oil drawn from the oil tank, an additional MAF oil filter was installed on the intake pipe.
In August, oil leakage from the oil tank into the engine crankcase during long periods of parking was eliminated by introducing an air hydraulic seal in the atmospheric tube that connected the crankcase, the oil tank, and the power cylinder of the engine protection mechanism.
In addition, to prevent malfunctions of the R‑10T (R‑10TM) relay regulator when operating the tank in hot climates, it was relocated from the engine‑transmission compartment to the fighting compartment, on the left side near the engine bulkhead.
Starting in November, the DP‑3B radiometer was used to measure gamma radiation dose rates inside and outside the tank. The instrument’s control panel was mounted on the front side plate to the left of the driver’s seat, while the external unit was installed at the junction of the left front side plate and the lower nose plate.
PT-76B Mod. 1966
Starting in March, to improve starting the engine and ensure more stable operation of the heater with the standardized blower, a heater boiler with an enlarged neck diameter of 90 mm was installed.
In May, the protection of the TShK‑66 scope was improved by using special armored covers and shields, which prevented lead splashes and bullet fragments from entering the turret through its embrasure.
To prevent exhaust gases from entering the vehicle through the intake tract when the engine’s crankshaft rotation direction was reversed, an electromechanical engine stop device (UOD) was introduced.
The main element of the UOD was a TD‑1 thermal sensor, installed in the air‑cleaning system before the engine’s intake manifold. In the event of a change in the crankshaft’s rotation direction, exhaust gases from the first explosions in the engine cylinders heated the “hot” junctions of the thermal sensor, which then sent a signal to trigger the engine‑transmission compartment pyropatron without activating the PPO cylinder.
PT-76B Mod. 1967
In January, to increase the rigidity of the rear part of the hull, the thickness of the lower rear plate was increased from 6 mm to 8 mm.
Starting in March, the ST‑713 starter was replaced with the ST‑721 starter, rated at 11 kW (15 hp), equipped with an inertial drive, designed for short‑term operation at 24 V, built in a dust‑ and splash‑proof version, and having reduced weight and dimensions.
At the same time, a new antenna device was introduced to prevent failures of the antenna input, and to avoid breakage of track links along the plate and of the track teeth at the window section, a new track design was adopted with the plate thickness increased by 1–2 mm and with solid teeth (without windows). Also, the SGMT coax machine gun was replaced with the Kalashnikov’s PKT coax machine gun. (note - Although no precise records could be found, It is more likely that from the 1970s onward, the pre 1967 PT-76’s SGMT was replaced with the PKT.)
In May, the R‑113 radio with the R‑120 intercom was replaced by the newer R‑123 radio with the R‑124 intercom.
In July, to eliminate cases of failure of the road wheels at the welded joint between the discs and the hub, reinforcing pads were added to the inner side of the discs and the weld seam was increased.
From 1952 to 1967, a total of 3,039 were produced.(This includes 10 units from the pilot batch of 1951, These initial 10 units were both prototypes and the pilot production, and they remained in military service until decommissioned.)
I could not find the exact month in 1967 when production was discontinued. Therefore, my personal guess (not official) is that it ended in either July 31 or August, September.
END.
Btw, In russian word, the сигнал(signal) has two meanings. one is the signal, and the other is car honker.)
