The USSR was always interested in tank building abroad. This is not surprising, like in any tank building nation its designers wanted to keep up with the competition. Foreign tanks often appeared in the USSR. Some of them were trophies (those turned up in the late 1930s), others came willingly. Among them was a Czechoslovakian LT vz. 35, which left a mark on Soviet tank building in the late 1930s.
In search of a potential client
The USSR began to develop a military relationship with Czechoslovakia early on. In the mid-1920s the USSR showed an interest in the KH-50 Kolohousenka tank developed with the participation of famous German engineer Joseph Vollmer. There is information of such a tank being tested in the USSR, but no documents confirming this have ever been found.
A new step in Soviet-Czechoslovakian military relations began in the mid-1930s. On May 16th, 1935, on the same day as the opening of Moscow's new subway, a mutual assistance treaty was signed between the USSR and Czechoslovakia. The treaty followed the increased military activity of Germany, where the Nazis came into power. On March 16th, 1935, two months prior, the Nazis transformed the Reichswehr into the Wehrmacht and introduced conscription in Germany. The Germans no longer concealed that new weapons and vehicles were being produced for its army in contravention of the Treaty of Versailles. Czechoslovakian leadership perfectly understood what this meant and a treaty with a powerful nation like the USSR was necessary for the small country to survive.
"Sh-IIa" tank diagram dated 1938.
The treaty defined mutually beneficial military cooperation. Each side had something to offer. Czechoslovakia was interested in the Soviet SB bomber. This was an exceptional aircraft for its time and no one on the world market could offer anything like it. Czechoslovakia produced its copy of the SB in 1937 under the name Avia B-71. Czechoslovakian industry, primarily Skoda, could offer a number of cannons. The most successful consequence of this cooperation was the production of the 76 mm model 1938 mountain gun, which was based on the Czechoslovakian 75 mm mountain gun. The Red Army also obtained the 210 mm Br-17 and 305 mm Br-18, copies of Czechoslovakian heavy guns.
In addition to the general description of the tank, Skoda offered details of its design.
Czechoslovakian tanks were also of interest to the USSR. Due to the rapidly increasing military power of its neighbour, Skoda and CKD's primary mission was to increase production of the LT vz. 35 (aka Skoda S-II-a) for the Czechoslovakian army. Production was off to a rough start. The first tanks were three months behind schedule and the tanks were not exceptionally reliable. The army declined to purchase any additional tanks of this type. At the same time, Skoda indeed produced a decent light tank with powerful armament and front armour that could protect from high caliber machine guns. The only analogue of the LT vz. 35 at the time was the aged Vickers Mk.E with inferior firepower and protection.
Not surprisingly, Skoda's product piqued the interest of many nations. The Romanians were the first, tanks built for them were indexed S-II-aR. However, there was a chance that Romania might not have received them. The situation escalated in the summer of 1938. Czechoslovakia was seriously preparing to go to war with Germany. Every tank was now worth its weight in gold, and the army desperately needed tracked fighting vehicles.
An album of photos taken at trials of the experimental S-II-a tank also ended up in the USSR. This tank later ended up in the Soviet Union as well.
War never came. Great Britain and France, Czechoslovakia's greatest allies, betrayed it and pressured it to give in to Hitler's demands. The Munich Agreement was signed because the two nations were not ready for war, and the USSR's offer to supply troops to Czechoslovakia frightened them, if anything. In this situation there was no longer a point to supply tanks for the army, and Czechoslovakia's industry switched over to exports.
Since the army lost interest in the LT vz. 35 even before that, Skoda began to build tanks for export before the Munich Agreement was signed. After the last tank was delivered to the army on April 8th, 1935, the company continued to work for foreign buyers. The S-II-a was not the only tank on offer, there was also the S-II-c medium tank. Also known as the T-21, it was based on the SP-II-b tank that failed trials and was written off by the military.
News about Skoda's export tanks reached the USSR in the summer of 1938. The USSR was seen as a potential client. Later, in 1939, CKD also gave detailed information about its tanks to the USSR. Skoda went much further than its competitors.
A couple's ride around Moscow
Preparations for a visit to the USSR began in August of 1938, the height of tension between Czechoslovakia and Germany. The Ministry of Defense (MNO) took a direct part in this trip. The delegation was headed by Colonel Oleg Prochazka, chief of the 7th Department of the MNO (arrested by the Germans in 1940 and executed in February of 1945) and Captain Jan Nemec. For the sake of secrecy, the delegation was split into two. Prochazka and Nemec left Prague on September 9th and arrived in Moscow on the 11th. The tanks and seven drivers left for Moscow on August 24th.
LT vz. 35 driving on a slope. The registration number was removed for the sake of secrecy. Late September 1938.
Two tanks were sent to Moscow by railroad. The first was the LT vz. 35 prototype which at that point had the registration number 13620. The tank was far from new and was useful perhaps as a general demonstration aid. The workhorse of the trials was the second tank, chassis number 53918 and serial number 13903. This was one of the last tanks built at Skoda on March 11th, 1938. It was assigned to the 2nd Tank Regiment located in Přáslavice.
The tank is driving up a slope.
When the tanks arrived they were sent to the NIABT proving grounds in Kubinka, where they were unloaded on September 8th. Two special garages were waiting for them. The doors were shut tight as soon as the tanks entered. This was done for the sake of secrecy. All arriving drivers were placed in different hotels. Trials began on September 14th. Even though both tanks were ready for trials, only the production tank was used. The serial number was painted over, again for the sake of secrecy. This can be seen in photos of the "Sh-IIa" tank. A T-26 mod. 1938 tank was assigned to accompany the vehicle, as it was the closest Soviet analogue.
The trials drew a crowd. This was the most advanced foreign tank tested in the USSR at that time.
Trials were split into several stages. The first studied the driving characteristics of the tank. The top speed on a highway was 36 kph, a little higher than officially claimed. The average speed on a highway was 29.09 kph, the tank spent 118 L per 100 km of driving. The average speed on dirt roads was 20.66 kph and 151 L of fuel per 100 km was expended. Off-road the average speed was 16.25 kph and 173 L per 100 km was used. The T-26 weighed about the same and had a less powerful engine. It attained a higher top speed, 38.4 kph on a highway, but its average speeds were lower: 23.8, 15.5, and 10 kph respectively.
An attempt to climb a sandy slope.
The results of mobility trials were also interesting. The Sh-IIa could not climb a 29 degree sandy slope due to insufficient traction. However, the T-26 slipped here as well. The situation repeated itself when tackling a short (15 m) 35 degree slope.
An attempt to climb a variable slope dirt hill was successful. The Czechoslovakian tank climbed it in 25 seconds, but the T-26 could not manage this due to insufficient traction. Further trials confirmed this. Obstacles that the Sh-IIa could barely defeat were impossible for the T-26. This was because the tank had a more powerful engine and wider tracks.
Driving on a sandy slope. The tank lost its left track soon after. The GAZ-21 pickup truck can be seen at the top of the photo, this vehicle was being tested at the same time.
The running gear of the foreign guest showed its superiority when driving on slopes. The tank could drive on a slope up to 30 degrees, successfully turn around, and return. The T-26 could drive at a slope of 8 degrees and the track was thrown when it tried to turn. The Sh-IIa also suffered a similar accident: at a slope of 20 degrees the tank sank in the ground after driving for 25 m and a track slipped off. Sand and rocks jammed between the tracks, drive sprockets, and idlers. The tank had to be towed out of this trap.
Crossing a water hazard. The Czechoslovakian and Soviet tanks performed about the same in water.
After it was done with the hills, the Czechoslovakian tank headed for the water. This was a ford across the Moscow river near the village of Agafonovo 0.8-0.9 m deep. The trials in the hills were also held near there. The T-26 didn't take part in these trials, but trials of a T-26 model 1937 were held here that same year, and the Soviet tank managed to cross the 0.82 m deep water. The Sh-IIa tank crossed the river six times. The water could enter the driver's vision slit. If it was closed the water did not enter, but the driver was also blinded. The guaranteed depth that could be traversed was 0.8 meters, but bigger depths could be crossed if the distance was short.
Trials in a swamp. The Czechoslovakian tank did not finish the test, but the T-26 was stuck after driving only 10 meters.
The next stage of trials was a swamp 0.5-0.55 m deep near the village of Krutitsa. Trials were held on September 29th, 1938, where the tank again had a companion. The Czechoslovakian tank went first. It could confidently move forward when the tracks were submerged up to 300 mm and could even still turn. Any deeper, and it could still move, but not turn. At a depth of 340 mm the tank bottomed out, went 8-10 m further, and was stuck. The attempt to reverse was not successful and a tractor had to be called in again. The tank drove for a total of 80 meters. The T-26 bottomed out after driving for 10 meters. The Soviet tank could not turn on swampy terrain at all.
Crossing a trench. The Czechoslovakian vehicle proved itself here, surpassing the T-26.
The tank also showed itself well when crossing artificial obstacles. 12 different types of obstacles were prepared: trenches, anti-tank ditches, etc. The Sh-IIa successfully negotiated most of them in early October. The limit of its abilities was a triangular trench 5.5 m wide, 1.5 m deep, and with a 1 m tall berm. The Soviet tank maxed out at a smaller obstacle: 4.1 m wide, 0.8 m deep, 0,8 m berm. The Czechoslovakian tank was also stopped by a trapezoidal trench 2.6 m wide, 1 m deep, and with a 1 m berm. The T-26 could not cross it either.
The testers noticed the additional road wheel in the front of the tank. Thanks to it, the suspension did not receive as many shocks.
Climbing over a 1 meter tall wall.
The tank was also tested against a tree barrier. It could knock down a pine tree with a trunk diameter of 32.5 cm but not a pine tree with a 41 cm diameter or an oak with a 27 cm diameter. The testers blamed the driver for this. The tank could easily break through bricks and climb a 1 meter tall wall. The T-26 was limited to 0.8 meters. The commission deemed the Czechoslovakian tank's mobility satisfactory and higher than the T-26's.
Penetration trials weer brief but showed that the Czechoslovakian armour needed improvements.
A few shots were made when testing the tank's armour. One of the tanks was shot at by the 12.7 mm DK machine gun from 100 meters. A number of hits resulted in dents, but there were a few complete penetrations. It also turned out that the tank's armour was produced from expensive chrome-nickel-molybdenum steel with 4.7% Ni content in the front armour and 1.9% in the sides. The armour was also very brittle. Specialists from the Izhora factory that tested the armour offered to improve it via cementation. 30 mm of Soviet armour was superior to 27 mm of Czechoslovakian armour.
The 37 mm Skoda A3 gun was tested against an MS-1 tank. The effectiveness was judged sufficient for its caliber. However, testers determined that a tank with this weight and dimensions could use an even more powerful gun.
The radio station. Its design was deemed simple, but the range was unsatisfactory.
Crew conditions were studied as well as individual elements of the tank. The optics were high quality and the sights were light. The presence of a mechanical backup sight was an asset in case the optical sight was disabled. The ammunition was stored well, but its number (73 rounds) was deemed insufficient.
The Soviet testers didn't like the periscopic sight. It was not fixed to the roof and it was impossible to use in motion. It is also worth mentioning that there was only one crewman in the turret. The commander's cupola was also judged poorly, as its air intakes were large enough that one could throw a grenade or a Molotov cocktail through them. The turret hatch was too heavy. The commander's seat was very uncomfortable, and the seats of all crewmen were less comfortable than those used on the T-26.
The machine gun belts were also deemed a drawback of the tank. The radio was considered simple to use, but its range was too low and the radio operator's station was cramped. The tank also drew in a lot of dust during driving. This was made worse by a lack of ventilation fans. In short, the Sh-IIa combined good and bad aspects.
A failed Czechoslovakian branch
The main goal of the visit to the USSR was the exploration of a possibility to sell tanks. Pilsen considered the USSR to be a more valuable client than Romania. The LT vz. 35 was a good tank, and later used by the German, Romanian, and Bulgarian armies. However, even the Czechoslovakian army had issues with it back in 1937. The MNO composed requirements for a new light tank on October 20th, 1937. CKD won this tender and its TNH-S tank was accepted as the LT vz. 38. However, the USSR didn't need help from abroad. Its industry was capable of supplying the army.
The same tank that was tested in the USSR, March of 1939. It was knocked out and captured by Hungarians.
Czechoslovakian documents remarked that the delegation was treated very well, but most specialists sent to Kubinka suspected that the USSR will copy their tank. This was a mistake, as the USSR had no interest in it. Even without the issues discovered in trials the tank was not suitable for any role defined by the Automotive and Armoured Vehicle Directorate of the Red Army (ABTU). Skoda offered the USSR a license for production, but that was not interesting either. The Soviet side wanted to purchase two sample tanks to study their components. Skoda declined and the tanks returned to Czechoslovakia.
The experimental tank was detained in Romania in the spring of 1939 and the production tank was knocked out in March of 1939 during a border conflict with Hungary. At least one crewman died and the tank was captured by the Hungarians. It later received the registration number 1H-407 and served as the only LT vz. 35 in the Hungarian army. Later Hungaria obtained a license to produce the Skoda T-21 under the name Turan.
A T-26-5 tank bogey.
Skoda's ideas found their use in the USSR in the summer of 1938, as soon as materials on the S-II-a were received. The idea was the modernization of the T-26's suspension. Trials showed that the running gear was not the Soviet tank's strong suit. It had an issue with throwing tracks, especially when driving on soft soil. The ground pressure also increased as the tank's mass grew. These issues were known but nothing could be done about it.
Experimental factory #185 worked on the issue. Information about the Czechoslovakian tank came in handy and the first variant of the modernized suspension was produced in August of 1938. It was built similarly to the S-II-a suspension, even including an extra road wheel to absorb impacts. This version did not last long. It turned out that this variant needs a lot of work as soon as the Czechoslovakian tanks reached the USSR. The ABTU demanded that ground pressure be reduced in December of 1938. This meant that a new wider track link was needed. Blueprints of a second variant of the suspension were ready in January of 1939. This variant was called T-26-3 in correspondence, but this was not the final change.
T-26-5 on trials. The NIABT proving grounds calls it T-26M, which introduced confusion.
Tactical-technical requirements for a new running gear were composed on February 2nd, 1939. These requirements formed the foundation for the third type of running gear. The layout was taken from the S-II-a and the track was widened. This variant was indexed T-26-4, and later the designation T-26-5 was used. Engineer-designer Zhukov worked on this design. This tank created some confusion. Proving grounds documents called it the T-26M, which created the sense that there were two vehicles with this suspension. In reality, the T-26-5 and T-26M are the same. In addition to new suspension and new running gear, it had new track links. The diameter of the return rollers grew from 254 mm to 280 mm, the road wheels grew from 305 to 340-350 mm, the track was widened from 260 to 350 mm. The drive sprockets were also changed.
The T-26's speed increased significantly with a new suspension.
The T-26-5 or T-26M underwent trials in July-August of 1939. The vehicle was built out of a production T-26-1 model 1939 with a conical turret and sloped turret platform. The tank drove for 313 km, 150 on a cobblestone road, 40.5 on a paved road, 115.2 on a dirt road, and 7 at the factory. The average technical speed ranged from 19.2 to 21.6 kph on the cobblestone highway and 27.9 kph on the paved highway. The average speed on dry dirt roads ranged from 20.6-24.3 kph. Defects were found during driving that were corrected before proving grounds trials.
The T-26M fared a lot better on slopes.
The tank drove for another 1000 km at the NIABT proving grounds, including 200 on a new cobblestone highway, 200 on a poorly maintained cobblestone highway, and 255 on a gravel road. The average movement speed was 26.74 kph. This was much higher than the average movement speed of the production T-26 tank tested in August-October of 1938. Due to overheating of the engine and frequent suspension issues its average speed was 19 kph.
Trials of the T-26M showed that some tracks bent inwards as a result of being hit with rocks. The T-26M travelled for 345 km on dirt roads, of which 254 were on iced over roads and 91 were on thawed roads. The average speed was 21.4 kph while the average speed of a T-26 in the same conditions was 15.2 kph.
The new running gear was more reliable and allowed the tank to drive at a lower RPM. The T-26M also performed better on slopes and hills, as well as swamps. The testers approved factory #185's suspension and recommended it for production. The same suspension was used on a T-26-1 tank designed at factory #174. However, the T-26 with a Czechoslovakian suspension never went into production. The T-26 was being removed from production and a torsion bar suspension seemed much more promising for new tanks.
Trials of light signals equipment, fall 1939.
Soviet engineers also noticed the light signal device on the turret hatch door. The three colour lamp was used as an alternative to signal flags. The device was installed on the roof of a T-26 tank and tested in October of 1939. The trials showed that the signals could be seen from 35-100 meters during the day. At night, the green light could be seen from 1000 m, the red light from 2000 m, and the white from 3000 m. The device was insufficiently sealed against water. As a result of the trials a recommendation was made that factory #174 improve its design, but in reality it was simply forgotten.
Transmission of the Sh-IIa. The planetary gearbox was used by Shashmurin when designing the gearbox for the KV-1 tank.
One little known fact is worth mentioning here. The famous designer N.F. Shashmurin mentioned in his memoirs that he studied the planetary gearbox of the Czechoslovakian tank. This design served as a foundation for the gearbox that Shashmurin designed for the KV-1 tank. At first, the planetary gearbox (third variant) was considered the priority for the KV-1, but later Dukhov's mechanical gearbox was put into production instead. Nevertheless, the history of the KV-1 has some Czechoslovakian roots.