The army always needs tanks that can cross water obstacles. There are two ways of solving this issue: the tank can either swim or drive underwater. The Soviet T-54 tank went with the second option.
The topic of researching and studying underwater driving equipment was a very important one at the NIIBT Proving Grounds after the war. Experience gathered during WW2 showed that it was important to find methods of crossing water obstacles as quickly as possible. The proving grounds at Kubinka became one of the main developers of various underwater driving systems.
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| T-54 tank with underwater driving equipment installed, three quarters view. |
Deputy Chair of the GBTU NTK Engineer-Colonel Kovalev approved the technical requirements for a set of underwater driving equipment for the T-54 tank in late 1952. The vehicle equipped with underwater driving gear was designed to capture or widen footholds on the other shore of water bodies. The requirements called for the tank to be able to cross a 300 m wide and 4 m deep obstacle.
The time required for the crew to prepare the tank for diving could not surpass 2 hours. The tank had to return to fighting shape 10-15 minutes after the crossing. The equipment had to supply enough air for the crew and engine to work normally. The seals were required to prevent enough water to impede the tank's function from seeping in. The total mass of the equipment had to be less than 250 kg and each individual component could weigh no more than 50 kg. The set of equipment had to comfortably fit into a truck.
Design work began in 1953. The wading equipment set included seals for the engine deck, turret ring, driver's hatch, gun mantlet and muzzle, sight opening, coaxial machine gun opening, and ventilation fan. An exhaust valve, water pump, and air intake pipe were also included.
The engine deck was waterproofed with a rubberized fabric sheet. A canvas liner was laid under it, as the sheet snagged on protruding engine deck components and tore during trials. The edges of the sheet were pressed against the hull with rubber lined clamps held on with bolts. On the left side the seal had an opening for the exhaust pipe. The exhaust pipe was sealed with an asbestos liner.
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| T-54 with underwater driving equipment installed, top rear view. |
15 bosses were welded onto the hull to attach the liner. One of the biggest drawbacks of this installation was that the external fuel tanks and oil tank had to be removed and their openings plugged. It was also unclear what to do with the tanks once removed, especially if there was still oil or fuel inside.
The turret seal also held on the engine deck sheet from the side of the turret. The turret seal consisted of an air tube circling the turret ring. Considering that the tube snagged and tore during previous trials, it was protected with a canvas liner. The liner had two slots: one for the tube and one for a rope that could hold the liner in place. The rope could be tightened with a clamp. There was also an opening in the liner for a valve to inflate the tube. The seal had to be installed carefully to seal the turret ring and avoid tearing the tube.
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| Engine deck seal. |
The driver's hatch was sealed with ZZK-2 paste. Only the hatch lid axle and ventilation opening had rubber seals. The gun mantlet was also sealed with rubberized fabric. The stock gun dust cover was used as a liner. The seal was also held with clamps on bolts with rubber liners. Springs were installed on the lower part of the liner to stretch it out.
The muzzle was sealed with a mechanical casing with a rubber cuff that was fixed to the barrel with a clamp. Barrels with a fume extractor and without had different casings.
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| Rope that held the turret ring seal. |
The sight and coaxial machine gun openings were sealed with metal shutters that were held on with brackets on bolts. The sight opening had one bracket and the machine gun opening had two. The machine gun flash suppressor had to be removed to fit the seal.
The fan opening was sealed with a steel casing held by rubberized clasps. Each clasp could be tightened with a nut to achieve a full seal.
An exhaust valve was mounted on the exhaust port with eight bolts. The exhaust port was sealed off with a rubberized asbestos gasket. Another such gasket was installed between the foundation and valve. When the engine worked underwater the gases pushed against the valve and exited into the water. When the tank was driving normally, the valve foundation was covered with a cap and the valve was stored in the tank.
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| Metal casing for sealing the barrel of a gun with a fume extractor. |
To prevent exhaust gases from reentering the tank, a separator between the air cleaner and exhaust was installed. This was a simple plank that could be opened or closed by the crew using a handle on the engine compartment bulkhead.
A pipe 142 mm in diameter was used to supply the crew with air. It was mounted on the loader's periscope opening. The steel pipe was sealed with a nut and a rubber liner. The pipe could be installed or removed from inside the turret.
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| Coaxial machine gun opening cover. |
A water pumping system with a radial flow pump and electric motor powered by the tank's electrical system was used to pump away water that seeped in. The use of a radial flow pump required the installation of a sealing valve that prevented water from entering the tank in case the pump was turned off. The valve was hend in a special casing on the cover of the maintenance hatch on the floor of the engine compartment. Interestingly enough, the pump itself was mounted in an ammunition rack cell on the left side of the fighting compartment. The round itself was temporarily loaded into the gun. Water was pumped out of a hose installed in the commander's hatch. The driver was responsible for turning the pump on and off. He had a switch for this purpose.
All other openings in the tank were sealed with ZZK-2 grease. The total weight of the underwater driving equipment was 144 kg, much less than the limit set in requirements.
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| Fan opening cover. |
Installation of the underwater driving equipment required some changes to be made to the design of the tank. In addition to the 15 bosses to mount the engine deck seal, the number of openings to hold the gun mantlet dust cover was increased, the opening for wiring of the running lights was moved down, the ventilation fan carrier shape and location were changed, three bosses were welded to the floor of the engine compartment to hold the locking valve of the water pump system, planks were welded to the turret platform, a tray was installed under the main friction clutch crown, the engine cooling fan casing was sealed, a stopper in the air cleaner was introduced, and wiring for the water pump was installed.
Two wrenches and a bicycle pump were added to the tank's toolkit for installation of the underwater driving equipment.
A full set of underwater driving equipment was produced at the proving grounds workshop and sent to the 18th Mechanized Division of the Kiev Military District by mid-1953. Preliminary trials of the equipment and a test crossing of the Dnieper was carried out there. The results of trials were satisfactory and the equipment was recommended for mass production. Factory #75 in Kharkov was chosen to produce it.
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| Exhaust valve. |
The NIIBT Proving Grounds adapted their technical documentation to the factory's abilities in 1954. The documentation was passed on to factory #75 in 1955. The factory then produced three sets of underwater driving equipment and prepared three tanks for installation. Mass production T-54 tanks built in 1954-1955 with serial numbers 5407Е015, 5505Е024, 5505Е028 were used for this purpose.
The tanks drove for 420-465 km before trials, after which they were modified and sent to the 18th Mechanized Division in Cherkassy where trials would be held. All three tanks were briefly tested at the factory to confirm that the equipment was installed according to requirements.
The main goal of the trials was to test the equipment in a 300 meter long and 5 meter deep crossing. The quality of the equipment and reliability of the seals was also checked.
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| T-54 tank driver in a waterproof gas mask. |
Engineering units of the 18th Mechanized Division thoroughly checked the crossing routes. Two areas of the Dnieper were identified as potential candidates. One was 340 m wide and up to 3.4 m deep. The stretch where the river was more than 2.5 m deep and the tank would be fully submerged was 184 m long. The river floor was sandy and the current flowed at a rate of 1 m/s. This was not a fully satisfactory trial since it did not have a depth of 4-5 meters. A secondary section of the river 150 mm wide with a depth of 5 meters was chosen. Due to a large amount of silt, only a 75 meter long stretch was considered serviceable. The air temperature on the day of the trials was 6-12 °С, the water temperature 6-8 °С.
The tanks drove underwater to test both the system as a whole and individual components. Tanks #015 and #024 crossed the river 5 and 6 times respectively, and #028 crossed it 12 times. Evacuation from a flooded tank was also practiced. The crews were equipped with IP-46 waterproof gas masks. To quickly pull out the tank, it was already linked to an AT-T tractor on the shore. The amount of water that would enter the tank if the turret ring seal was punctured was also measured.
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| One of the tanks enters the river. |
A mobile diving station on a BAV-485 amphibious car, BMK-90 tugboat, and two tractors (the aforementioned AT-T and a BTS-2) were present to ensure the safety of the trial participants.
All tanks drove for 55-65 km during the trials, including moving from the train station to the trials area. This counted for 5.5-7 hours of engine runtime.
The tanks were prepared for crossing water obstacles before the trials. The presence of all seals and shutters as well as their tightness was checked. All electrical system openings, machine gun opening plug, smoke bomb wiring openings, commander's cupola slits and bearing race, as well as the gunner and driver's observation devices were packed and sealed with ZZK-2 grease. The external fuel and oil tanks were removed and their fuel lines were plugged. The engine deck, gun mantlet, firing port, ventilation fan, gun muzzle, and turret ring seals were installed. The suspension swing arm slots were also greased. Valves were also added to the exhaust pipe and air intake pipe.
An escape pipe was also installed on each tank for safety.
It turned out that it was impossible to keep to the recommended pressure in the turret ring sealing tube when inflating it. All crewmen had to enter through the loader's hatch since the other hatches were sealed with ZZK-2 grease. After this, the loader's hatch was sealed with grease from the outside. This was not the best solution since the crew would not be able to prepare their tank for underwater driving on their own. Each vehicle took 3-3.5 kg of grease to seal.
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| Driving at a depth of 4.5 meters. |
It took about 90-105 minutes to prepare a T-54 tank for underwater driving. Each tank drove to a depth of 5 meters in turn. At first, the crew drove to a depth of 1.4-1.5 meters and the driver shut off the engine. The crew then watched for leaks. If none were detected, the tank would then drive to a depth of 4 meters. There the crew would again watch for leaks. Upon completion of the trial the tank was pulled back to shore with a winch.
Small leaks were observed on all three vehicles, especially through the driver and commander's hatches. In addition, tank #024 had leaks through the gun mantlet seal and tank #015 had a leak through the asbestos seal on the exhaust pipe. Each tank gathered about 25-30 L of water after being submerged for 15 minutes. After extraction, all leaks were corrected with a thicker layer of ZZK-2 grease.
The only seal to not still leak was the asbestos seal on tank #015. This tank also had water in the exhaust pipe, fume extractor, and air cleaner due to faulty valve plates. After this issue was corrected the valves worked normally.
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| A rescue tank approaches a "stalled" tank. The "stalled" tank has a fume extractor on its barrel, the rescue tank does not. Note the difference in seals. |
After preliminary checks and corrections of bad seals the tanks drove to a depth of 4.5-5 meters. All sets of equipment worked reliably and the engines started underwater on the first try. There were no more faults with the equipment. The penetration of exhaust fumes into the crew compartment was tested. The tests showed that the shutter worked reliably. Before this the concentration of CO₂ in the crew compartment was tested at the factory, showing that fumes were far below the acceptable limit.
The tanks used their regular communication and control equipment during trials. The antennas were not insulated in any special way. The radio worked reliably even if the entire 4 meter long radio antenna was submerged.
A small defect was found in the water pump system. The pump only turned on with the second press of the switch. There was a suspicion that an air plug was forming somewhere. The pump extracted 40-45 L per minute at a depth of 5 meters and 75-80 L per minute at 2.5 meters.
To test how much water would enter the tank if the turret seal was punctured, one tank submerged to a depth of 4.2 meters with a deflated tube. The water began to trickle through the turret ring at a depth of 2 meters and streamed in at 4 meters. The tank took on 220 L of water in 8 minutes. The conclusion was that a puncture in the tube would not result in an emergency and the water pump could deal with the flow of water.
Initially the tanks crossed the trials area in 6 minutes, which corresponded to an average speed of 3.7-4.1 kph. The drivers were being overly careful and driving slower than they could be. Later runs gave an average speed of 5.8-6 kph. The current offset the tanks' course, but the driver could easily correct for it with the guidance of the commander. If the tank was driving with an evacuation pipe, then the tester that acted as the tank commander could give directions using the tank's intercom. If not, corrections were given over the radio.
All tanks took on water during the crossing of the Dnieper. One crossing resulted in 10-15 L of water entering the tank. There were some unpleasant moments, for instance during trials of tank #015 water entered the driver's observation device. Water entered the headlights and signal lights on all tanks, disabling them.
The underwater driving equipment was deemed to be sufficiently reliable and could be reused after the trials. Two tanks had their fenders dented during the trials.
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| A diver hooks up tow cables between the two tanks. The towing tank has an evacuation pipe. |
The antifreeze and oil temperature in the engines did not exceed acceptable parameters. Tank #028 that crossed the Dnieper once and then doubled back, crossing a total of 700 meters, never had its oil heat up more than 90 degrees. The conclusion was that a T-54 tank could confidently drive underwater for 500-700 meters.
The crew's working conditions were a bit worse than on land, but remained satisfactory. The only significant issue was that the pump hose got in the way of the commander using his observation devices.
In the end of the trials, the crews tested the evacuation of a tank from under the surface of the river. A diver hooked the two tanks together using tow cables. This operation was timed. It turned out that the most complicated part was getting the cable to a tank that was left a large distance from the shore (200-300 meters), and so a shortcut was taken. The towing tank had a tow cable stowed on its front as normal. This tank was then connected with a cable to the AT-T tractor's winch on shore.
The "stalled" tank was left at a depth of 2.3 meters. Its tow cables were stowed normally. The towing tank approached to a distance of 1-1.5 meters. A BAV-485 amphibious car dropped anchor nearby and deployed a diver. It took 18 minutes to link the two tanks together, after which the evacuation began. The evacuated tank was fully operational and no issues cropped up during recovery. This method was recommended for use in the army.
Tests were carried out on land to see how far a tank could drive after seals have been installed. The engine began to overheat after driving for 2-2.5 km. A compromise was proposed where tanks could be driven from further positions with all the seals installed except the rear engine deck seal clamp. It only took two crewmen 2 minutes to tighten the clamp after that.
An incident occurred during the trials when opening the engine cooling shutters tore the seal from the engine deck roof. Instructions were amended to prohibit the opening of the engine cooling shutters even if the engine was reaching critical temperatures.
It was necessary to remove the underwater driving equipment after the tank crossed the river. Depending on the situation, it was possible to either fully remove the equipment or only partially remove it. In cases of partial removal, only the seals that inhibited aimed firing and lengthy marches were removed. Damaging individual components of the underwater driving equipment was permitted. In either case, the crew had to exit the tank.
Partial removal consisted of removal of the sight opening cover, gun muzzle cover, turret ring seal, air intake pipe, and exhaust pipe seal. The engine deck seal was simply cut open. The water pump hose was removed, the air cleaner shutter was opened, and the seal in the commander's hatch was pulled out. This only took 2-3 minutes, after which the tank was ready for action. It took 10-12 minutes to fully remove the underwater diving equipment. In this case, the engine deck cover was carefully removed, the coaxial machine gun opening shutter and ventilation fan cover were also removed. The loader's hatch was unsealed and his observation device was returned.
These trials and the ones carried out earlier revealed a nuance of underwater driving. The crew had to conduct additional service of the tank as soon as possible: replace the grease in the final drives if water was found there, remove the ZZK-2 grease seals, oil the suspension swing arm sockets, wipe down and oil all tools stowed on the fenders, return all fuel and oil tanks to their original locations, drain water from the lights, observation devices, and turret ring, wipe down the external electrical equipment and radio. Finally, the underwater driving gear had to be wiped down, oiled, and stowed.
After trials were completed, a demonstration of the underwater driving equipment was staged for the officers of the 18th Motorized Division.
Overall, the trials of the underwater driving equipment were deemed a success. The underwater driving equipment set designed by the NIIBT Proving Grounds and produced by factory #75 allowed the T-54 to cross bodies of water 500-700 meters wide and up to 4-5 meters deep. The equipment was recommended for mass production after defects were corrected.
Recommendations for changes before mass production included using a tougher material for the engine deck and gun mantlet seals to avoid the need for canvas liners. The use of a one piece turret sealing tube with a motorcycle type tire valve was recommended. To control air pressure in the tube a manometer was to be introduced into the tank's toolkit. The muzzle seal and ventilation cap seal had to be made from rubberized fabric instead of metal, since the metal shutters were too bulky. In case the tank submerged lower than 5 meters or the ventilation pipe was damaged, it also had to have a shutter.
The shape of the external fuel tanks was to be revised and their pipes be shifted downwards in order to not interfere with installation of the engine deck seal. The oil tank had to be turned 90 degrees for the same reason. An instruction placard for the crew on how to use the air cleaner shutter also had to be installed. The driver's intercom cable had to be lengthened to permit it to reach the A1 device. The most important thing was the development of a user manual on how to install use the underwater driving equipment. All crews also had to be trained on the IP-46 waterproof gas mask. The gas masks and flotation vests would be introduced into the vehicle's standard equipment set.
Changes in the T-54 tank's design connected to the installation of the underwater driving gear were to be implemented into production in 1956. Exercises would also be held that same year where a whole regiment of tanks would cross a body of water.