Saturday, 14 December 2019

Tanks to Sleds

GKO decree #1958ss "On production of T-34 and T-70 tanks" was published on July 3rd, 1942. According to this decree, production of T-60 small tanks ceased as of July 5th. By this point these tanks were in production at factories #264 and #37. The first factory, located in Stalingrad, switched to producing hulls for T-34 tanks. Factory #37 in Sverdlovsk switched to the T-70, but not for long: T-34 production started here as well.  

This is usually where the tale of the T-60 tank ends. However, that is not the end of the story. In late 1942 - early 1943 Soviet industry continued to build products made from T-60 armoured hulls. These were armoured sleds, work on which began in early 1942.

Overweight cart

The Red Army began thinking about building APCs in the 1930s, but work did not proceed past some experiments. A certain APC-like vehicle was used in the Winter War. These were Sokolov armoured sleds, which allowed infantry to remain protected while accompanying tanks. 300 sleds of this type were in storage by spring of 1941. The topic was revisited in late 1941. The Department of Inventions of the Main Automotive and Armoured Directorate of the Red Army (GABTU) was flooded with proposals for armoured sleds of various types.

There were some exotic designs among them. A designer from factory #112 V.E. Gubanov proposed an armoured assault trailer in late February of 1942. It consisted of a shortened T-34 hull with the same armament and armour. In the summer the trailer retained its tracks, in the winter the tracks were replaced with skis. According to the author's calculations, the trailer would weigh 10-15 tons. These sleds could be developed in three variants: combat, combat assault, and special type.

According to the author, the trailer could be designed and built at factory #112 in a short time. To make work faster, ordinary T-34 hulls could be used. In this case, the mass would increased to 15-20 tons, but the amount of troops carried would increase from 10 to 15.

BDTP armoured trailer, February 1942. The author was too optimistic in his calculations. It is not likely that the T-34 would be able to tow such a huge weight.

The BDTP was reviewed on February 27th, 1942, by the 5th department of the GABTU. The same meeting discussed the B-65 armoured sled developed at factory #592. These 20 ton sleds could barely be towed by even a KV-1 tank. Commanders and technical deputy commanders from the 31st, 33rd, 62nd, and 143rd Tank Brigades with experience in winter combat were invited to discuss the designs.
They unanimously declined these huge trailers. A conclusion was composed as a result of the meeting.

"
  1. The 15-20 ton trailers proposed by factories #112 and #592 are not acceptable. The KV tank does not have the final drive or main clutch reserve to operate with them, and the T-34 will be at its limit.
  2. To provide protection for the tank rider company of the tank brigade, it is desirable to develop a trailer for the T-34 tank with the following characteristics: 
    1. Weight: 5 tons
    2. Crew: 15
    3. Armour: 13-15 mm
    4. Firing ports:
      1. 5 per side
      2. 2 in the rear
      3. 2 in the front
    5. Height: 1.5-1.6 meters
    6. Width: same as the tank
    7. Exits: rear, sides, floor
    8. Running gear: wheels and tracks
    9. Unhooking mechanism in the tank
    10. Rear tow hook
    11. Visibility: mirror periscopes along the sides, front, and rear
    12. Ground pressure: no higher than the tank
  3. Amount of trailers per tank brigade: 5
  4. It is reasonable to use BT tank hulls without the turret and engine, converting them to meet the assault trailer requirements.
  5. It is desirable to include tractors into the tank brigade to tow the trailers, one tractor per two trailers."
This document contained the first requirements for an armoured sled. The meeting participants did not shy away from the idea of using existing tank hulls. However, everyone present understood that the mass of the trailer had to be radically decreased. As further events showed, this was a reasonable requirement.

TD tank trailer, February 1942.

Analysis and study of various inventions that were sent to Moscow during the war is treated as a waste of time by many. This is not the case. Of course, most proposals submitted by citizens were impossible, but even the 1% of successful ideas made the paperwork worth it. One of these rare proposals was sent to Moscow from Chelyabinsk on February 16th, 1942. Its author was the deputy chief metallurgist at factory #78 D.I. Chizhikov. In a letter addressed to Stalin Chizhikov described an armoured trailer that used the T-60 tank running gear.
"For deployment of troops in the enemy rear, use tracked armoured trailers (TD) (tank desant, mobile pillbox".
The TD trailers can also be used as pillboxes, ammunition carriers, ambulances. The TD is not a difficult transport to produce. It consists of a simple hull and suspension on tracks with no engine. 
The TD hull can be made from steel by either welding, riveting, or casting. The TD can be built using small armour plates with defects that were rejected during tank production. Components from knocked out tanks or those rejected during production can be used to make the running gear. Tractor parts, such as those from the S-2 ChTZ tractor, can also be used.
As the TD is a very simple design, production can be set up in a short time at any factory, no matter how limited in its ability.
I asked the director of factory #200 (Izhora factory in Chelyabinsk) comrade M.N. Popov for help in the development, and he reacted positively, immediately allotting designers. Currently the TD variant built from the T-60 tank is finished. One TD can be built for trials."

Chizhikov's idea turned out to be much more realistic than the previous proposals. The TD was 4.5 meters long, 2 meters wide, 1 meter tall. The suspension and running gear came from the T-60 tank. The armour and capacity of Chizhikov's trailer surpassed the desires of the military: the sides were 40 mm thick, the front and rear were 30 mm thick, the roof was 20 mm and the floor was 15 mm. The TD fit 25 riflemen who could fire out of 14 portholes. The mass of the trailer was estimated at 9 tons, and a KV tank was proposed as the tractor. It could be built at factory #200, which was formed out of factory #78 in 1941 to produce KV turrets.

The TD-200. This variant was built in metal.

One advantage of the design was that it was based on existing components. Even in Chizhikov's initial proposal, the vehicle seemed very attractive. Factory #200 was also an interested party, especially financially. The actual developers were its engineers, and not the deputy chief metallurgist of factory #78. "Foreign" projects were never welcomed at any factory, unlike "local" ones.

It is not surprising that factory #200 received Chizhikov's idea with enthusiasm. The TD project at factory #200 was led by senior designer Krasilnikov and design bureau chief Sergeyev. The name of the trailer changed to TD-200, where 200 stood for the factory where it was being developed. Chizhikov played the role of a consultant and promoted his brain child, bombarding various organizations with letters in case of delays. At the same time, his name is not mentioned in discussions of the project.

TD-200 at factory #200, spring 1942.

According to senior military representative 2nd class Pestov, by March 20th the factory was building three TD-200 prototypes.
"Production and trials will be completed on March 20-22nd, after which they will be sent out with one of the units being formed at the Kirov factory. This is approved by the regional engineer. 
The early trailers use the running gear of the T-60 tank because it was the easiest to obtain. In the future it is necessary to use tractor type running gear, for instance from the STZ-HTZ tractor, to reduce cost.
It is also necessary to test the armour thickness used, whether the portholes are sufficient or ball mounts are needed, if observation devices are needed, how fast can the hatches be used, etc.
On my side, I think that the trailers are necessary for the Red Army and mass production should be arranged after their first use in battle, especially since various armour available in Kuznets and Magnetogorsk with defects and chemical deviations can be used.
I will do all I can to ensure that these trailers are produced and sent to the front as fast as possible." 
The same trailer from the rear.

The characteristics of the prototypes largely matched those proposed by Chizhikov. The infantry entered and exited the trailer through hatches in the front, rear and the roof. Another evacuation hatch was added in the floor. According to the GABTU's requirements, the TD-200 had to be able to drop off infantry through the rear hatch both while stationary and in motion. The infantry sat inside on benches that fit 5 men each. Tow hooks similar to the ones used on the KV tank but shorter were installed on the front and rear. A tow bar was mounted to them. The TD-200 had 10 portholes for fire: 3 per side, 2 in the front, and 2 in the back. The portholes were closed by sliding covers.

Hatches and portholes are open.

Factory trials of the TD-200 began on April 26th. The average towing speed behind a KV-1 tank was 16 kph. The trailer was towed for 48 km, 37 of them on a cobblestone road and 11 off-road. There were two cases where tracks slipped off: one when reversing at 75 degrees, one when moving forward at 50 degrees. The tracks were also poorly tightened. It was impossible to drop the trailer while moving, and 30 cm of clearance proved too little. It also turned out that the portholes could be opened from outside. After trials the prototype's single piece hatches were changed, which introduced a month-long delay. Worried about his creation, Chizhikov wrote another letter to Stalin asking to help speed up the work, but this had no effect.

Trials in May of 1942.

The second stage of the trials, conducted from May 19th to May 25th, took place at the same time as exercises at the Chelyabinsk tank proving grounds. This time the trailer was towed for 28 km. The TD-200 was tested at full load with 20 troops. It took 60 seconds to embark. The riflemen could successfully exit at a speed of 4-5 kph. The trailer was tested at full load off-road, 2 pits 1 meter deep and 4 pits 1.2 meters deep were successfully negotiated. To make the test more difficult, a 25 cm thick log was placed between the tank and the trailer. This obstacle was crossed twice at low speed. The tow bar was bent during trials, and a rock became lodged between the track and right fender, which bent it. One track tooth was bent while negotiating an obstacle, and one road wheel rim was damaged as a result. However, not a single instance of slipping tracks was recorded.

Factory trials concluded on June 15th. Inspection of the running gear showed that all parts were within tolerances. The trailer successfully passed factory trials. The second and third prototypes were completed in May and delivered in early June.

The tow bar and cable that was used to unhook the trailer from the tank can be seen.

Work stalled after that. There was no official rejection of the TD-200, but these trailers do not appear in correspondence any more. It is possible that the mass was too great, since the requirements composed by the GABTU in February of 1942 were still in effect. Finances could also have had an effect. The overall cost of the three trailers was 126,000 rubles, or 42,000 rubles each. Considering that the trailers were supposed to be built from byproducts of T-60 production, this was not very logical, as a whole T-60 cost not much more than that.

The suspension at work.

In addition to the TD-200, factory #200 developed the GHP chemical trailer. The design was very similar to the TD-200, but instead of an armoured capsule for the infantry the GHP mounted a contained for smoke or poison gas tanks. The gas was deployed from the rear. The GHP was offered in three different variations, differing in internal layout and size of tanks.

GHP chemical trailer, June 1942.

The GHP was reviewed by the 4th department of the Main Military Chemical Directorate (GVHU). The conclusion was ready by July 3rd, and it was not in favour of this idea. The T-60 chassis was in deficit, especially the tracks, as many T-60s stood idle without them. The GHP was also not cheap. Further development was declined.

TD-2, an attempt to make a smaller TD-200.

Only several days later, on July 5th, 1942, a letter from factory #200's chief engineer L.I. Eiranov arrived at the office of GABTU chief Lieutenant General Ya.N. Fedorenko. He proposed two more types of armoured trailers, indexed TD-2 and TD-3. This was the last attempt at saving the project. The proposal was nothing new: factory #200 pitched the same TD-200 but smaller. The TD-2 weighed 5750 kg and carried 15 men. The number of road wheels was reduced to 3. The TD-3 carried 20 men, and was heavier at 7850 kg. Like the TD-200, this trailer had 4 wheels per side.

The 20-man TD-3. Like the TD-2, it was not needed.

Initially, a prototype of the TD-3 was requested, but after Fedorenko examined the letter he ordered that only a TD-2 be built. The characteristics of the TD-3, like those of its predecessor, did not meet the requirements of the military. As for the TD-2, it received a green light. P.K. Voroshilov was responsible for its development. According to his report, the experimental trailer was ready by October 10th and went through factory trials. However, the idea of building trailers using the hulls of tanks removed from service was already raised. The Chelyabinsk trailers still had the chance to fight. Three experimental TD-200 trailers were sent to the 19th Tank Brigade, which also tried out experimental night vision devices. Alas, the trailers are not mentioned in the brigade's documents.

From existing stock

The end of work on Chelyabinsk trailers did not mean that this topic was closed. However, building of dedicated trailers was deemed an expensive endeavour. On September 11th, 1942, tactical-technical requirements for "armoured tank sleds" were composed.
"Towed tank sleds are designed to transport soldiers through enemy defenses and transporting assault teams into the enemy rear.
Consider the following requirements:

  1. The height must be no more than 650 mm.
  2. The armour must protect the troops from rifle fire at any distance and angle.
  3. The sleds must be protected with armour from all sides.
  4. The hatches must provide quick exit without subjecting the troops to enemy fire.
  5. Develop a towing device that can be used at an angle and tilt and disconnect from inside the tank.
  6. Include portholes in the front and sides for rifle fire. 
  7. The sleds should fit 16-20 men lying down. The maximum width of the sleds cannot be more than the size of the tank.
  8. The floor of the sled needs to have two grooves to protect them from slipping.
  9. The sleds must be reliable.
  10. The sleds should be transportable in trucks when disassembled.
  11. The front armour must not collect snow in front of it, but direct it downwards."
Some requirements proved impossible. 16-20 men shoulder to shoulder was not the way to go. The mass of an empty trailer was limited to 2500 kg, its width to 2200 mm. The technical characteristics resulted in the creation of a new generation of armoured sleds. The T-60 tank, recently removed from production, proved to be a suitable donor. By November 11th 212 T-60 hulls and turrets collected at the Molotov GAZ factory, plus 120 T-30 hulls and 50 turrets. With these stocks, the idea of a T-60 sled seemed tempting. The production cost would be minimal, the sleds would be cheap, and the issue of excess stock would be resolved.


DP sled draft.

Representatives of the Auto-Tractor Scientific Institute (NATI) approached the GABTU with the idea of an armoured sled on the T-60 chassis in September of 1942. A draft was completed by September 16th. The DP-60 developed by NATI engineers L.F. Kiselev and V.F. Goranov was reviewed by the GABTU. The project was pitched in three variants. The version weighing 3.3 tons was the most interesting. The design was based on the T-60's hull with portholes and a hatch in the rear. This variant fit 8 men. Initially, the GABTU considered the variant that retained its turret more promising.

The final variant of the NATI trailer, October 6th, 1942.

The final variant was prepared in early October 1942. The armoured trailer indexed BP had a mass of 3.5 tons. Its capacity increased to 10-12 men. In addition to infantry, it could carry 10-12 fuel barrels. A T-34 tank was used as the tractor. A special tow bar was hooked up to the rear tow hooks and the front of the trailer. If necessary, the crew of the trailer could disengage the tow bar without leaving the trailer.

Analogous designs were developed at two other organizations. On September 29th a letter was sent to  the director of factory #180 proposing the development of 4 experimental trailers for the T-34 tank based on the T-60 hull. A similar proposal was sent by People's Commissar of Medium Machinebuilding Akopov to the GAZ. In correspondence GAZ calls this product "armoured sled", and only one letter gives its index: BP-60.

A T-34 with two BP-60 trailers on trials.

Like in Saratov, the development at GAZ was done with the help of NATI engineers. According to correspondence, blueprints of the BP-60 were sent to the GAZ on October 22nd, 1942 and to factory #180 on October 30th. The armoured sled consisted of a T-60 tank hull on two wooden beams. Steel strips attached to the bottom formed the runners. The T-60 hull was modified as follows:
  • The turret ring was covered up with an armoured panel. The final drive openings, torsion bar ports, and air intakes were also welded shut.
  • A 1080x670 mm hatch was cut into the rear of the hull with two-piece doors that had hinges at the top. The crew entered and exited the sled from here. The driver's hatch was also preserved for this purpose.
  • Three firing ports with shutters were cut into each side at a height of 670 mm. The shutters could be opened and closed from inside the hull. Two ports were cut in the rear. The driver's hatch was used to fire forward.
  • A rope was attached to the roof along the middle for the riders to hold on to.
  • Two hooks were attached to the roof that could be used to tow a second sled.
The mass of the sled was 4 tons, which met the GABTU's requirements. Two sleds could be towed behind a T-34, with 20 riflemen in total. The sleds hooked up to the T-34 with a tow bar made from steel pipes. A lock with a cable leading to it allowed the sled crew to unhook itself from the tank.


The same "train" from the back.

The first four samples were produced at factory #180 towards the end of November of 1942. Work was supervised by NATI senior designer Garanov, one of the project authors. The sleds were produced in two variants with different tow links. One had hooks and another had loops. A meeting was held on November 27th, as a result of which changes were made to the sleds. The runners were lengthened in the front and back, the tow links changes, the rear loops were reinforced. Garanov was later sent to the Molotov GAZ factory where he took part in preparing for production of the sleds. The first production BP-60 sleds were finished in January of 1943.

Fields of fire from the sled.

The armoured sled was to be tested in motion behind a tank (25 km on a road and 25 km off-road). Tactical exercises with three sleds were also planned to determine their suitability as mobile bunkers. Trials held on January 13th-14th at the NIIBT proving grounds at Kubinka had to be shortened. The tow bar was bent when determining the minimum turning radius.

Two trials were held: one with two sleds lasting 5 km, one with one sled for 3 km. In both cases the sleds were fully loaded. The T-34 could confidently tow one or two sleds. The average speed was 25 kph on a road and 20 kph off-road in 400 mm deep snow. Trials showed that if turns tighter than 20 meters are made then the tow bar bends and tow hooks are torn off.

#2 indicates the cable that the sled crew could use to disengage from the tank.

Trials showed that a crew of 10 men with weapons could embark in 20-25 seconds and disembark in 30-35 seconds. The design of the hatches with hinges on the sides was deemed to be poor and it was recommended for it to be changed. The crew sat on the floor (due to the T-60's low height there were no seats), which was uncomfortable, but no excess shaking was detected during trials. Using the firing ports was convenient.

However, when towing the sled along snow covered dirt roads or off road, a cloud of snow was kicked up that made aimed fire from the portholes impossible. Trials also showed the fields of fire from the sled.

The rear hatch doors are raised.

Despite the defects discovered during trials, the verdict was positive:
  1. The proposed armoured sled can be used to transport 10 men or as an immobile firing post.
  2. It is possible to transport two sleds with one T-34 tank.
  3. The design of the tow bar makes it possible to disengage it on the move.
  4. The design of the tow bar makes it impossible to turn at a radius of under 20 meters.
  5. The armoured sled can be recommended into service with the Red Army, contingent on the correction of the defects outlined in the "trials results" section.
Finally, the armoured sleds were greenlit. Production began at GAZ in late January of 1943. Production in Saratov started in January as well. In addition to T-60 sleds, factory #180 produced 18 sleds based on the T-50 tank hull. The sleds were first used in the army before production began. According to the GABTU, T-60 sleds were used successfully by the 65th Army in the fall-winter of 1942 (likely these were leftover hulls from factory #264) on runners towed by tanks.


Process of exiting from the sled.

As of March 3rd, 1943, the Molotov GAZ factory finished 250 sleds, 35 of which were sent to the 1st Tank Army, 75 to the Western Front, 41 to the North-Western Front. Factory #180 produced 24 units for the Kalinin Front. As of December 21st, 1943, 120 sleds were present in warehouses that were headed to the front: 60 for the 2nd Baltic Front, 30 for the 1st Baltic Front, 30 for the Belorussian Front. The exact number of BP-60 sleds produced is not known, but the total production of factory #180 and the GAZ was approximately 300 units. Unfortunately, no details about their use in combat are available. The idea turned out to be very interesting. Similar designs were developed in other countries, but they pale in comparison to the BP-60.


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