Return to tracks
In the 1920s, Czechoslovakian tank developers, like many others, were drawn to the wheeled-tracked combination. Two Kolohousenka KH.50 chassis were built in 1923, built on the base of the German Hanomag WD-50PS tractor. The main feature of the Kolohousenka was the wheeled drive designed by German engineer Heinrich Folmer. Two improved prototypes followed, the KH.60 and KH.70. The speed on tracks was limited by the tractor chassis, ranging from 15 kph (KH.50) to 20 kph (KH.70). On wheels, the maximum speed increased to 35 and 60 kph respectively. However, this convertible drive made the design very complicated.
In 1929, the Czechoslovakian military abandoned the Kolohousenka program, but not the concept of a convertible drive tank. That same year, requirements for a "combined medium strike vehicle" (Kombinovaný střední útočný, KSU) were announced. Skoda answered the call. It's worth noting that the Laurin a Klement company, bought by Skoda in 1925, worked on the Kolohousenka program. On the other hand, Skoda based their tank production in their main factory in Pilsen, not in former Laurin a Klement factories in Mlada Boleslav. That was also the home of their design bureau. Ringhoffer-Tatra, also a participant in the Kolohousenka program, later submitted a competing project. The Tatra project was named "combined strike vehicle" (Kombinovany utočneny voz, KUV).
The KSU concept was approved in July of 1931, and a draft project was ready by that November. Unlike Kolohousenka, the wheels were inside the hull, not outside. The project had two armament options: a 37 mm gun or a 70 mm howitzer, as well as two machineguns. Ths 16.5 ton tank would be propelled by two 4-cylinder engines. The KUV would have a similar design. According do documents, Skoda received an order for two KSU prototypes on May 29th, 1933. They were due by December of that year. Tatra received an order for two KUV prototypes, due by September 30th, 1933.
These plans were not meant to be. As the project went on, it became clearer and clearer that the convertible drive is a dead end. The only viable solution to this problem was Christie's design, and even he gave up on it in 1936. Due to more powerful engines and improved suspension designs, tanks could reach 35-40 kph on tracks. This was enough, considering that a marching mechanized column would usually not go faster than 25 kph. In this situation, there was no need for a convertible drive. It was much more reasonable to return to a purely tracked design, using the gains in mass to improve armour. As a result, it was decided to cancel all convertible drive medium tanks.
According to the classification of the early 1930s, Czechoslovakian fighting vehicles were split into four classes:
- I: tankettes
- II: light cavalry tanks with 37 mm guns and 15 mm armour
- II-a: light cavalry tanks with front armour increased to 25 mm
- II-b: light infantry tanks with 25 mm of armour all around
In 1934, another category was added: III. This category included medium tanks with armour up to 37 mm thick. They were to be armed with a 47 mm gun. These tanks were designed to fight enemy tanks and light fortifications. KSU and KUV projects, which turned into the Skoda S-III and Tatra T-III, belonged to this category.
Infantry into Medium
Work on the T-III and S-III dragged on due to numerous changes to requirements. Tatra was the first to handle their task, and two T-III prototypes were finished by March of 1936. Many defects were discovered in trials, and their correction took until 1936. Skoda finished the first S-III in the end of 1936, and another in early 1937. It's worth noting that Skoda was supposed to provide turrets for both prototypes, but they only made one T-III turret. Due to technical problems, the S-III caught up to its competitor, and the two vehicles underwent trials together.
By then, the military not only had time to lose faith in the Tatra and Skoda designs, but order their replacements. S-II-b and P-II-b infantry tanks started trials in 1936. The first was a further evolution of the S-II-a cavalry tank, adopted by the army as LT vz. 35. The second tank, developed by CKD, was an improved P-II (also known as LT vz. 34). The competition didn't pan out, as neither vehicle was satisfactory. It was decided that the competitors' efforts should be combined, giving birth to the SP-II-b. The initial specifications mirrored a category II-b tank: 25 mm of armour, 37 mm gun, mass of about 13 tons. The requirements for the SP-II-b were submitted on June 30th, 1936, but were significantly changed by the end of the year. It was obvious that neither the S-III nor T-III were capable of taking on the medium tank role. The correct solution was to turn the infantry tank into a medium.
The new tank, jointly developed by CKD and Skoda, was made according to requirements from category III: 16 tons, 47 mm gun, 32 mm of armour. The companies divided up the work, developing individual components. CKD took on the engine, transmission, and hull. A new 14 liter 8 cylinder V-shaped Praha NR 200 hp engine was designed for this tank. The transmission was placed in the rear of the hull. The hull itself was an evolution of the P-II-b hull, whose transmission was also in the rear.
Skoda was tasked with assembly of the SP-II-b, as well as the suspension, armament, and turret. Pilsen engineers decided to not re-invent the wheel and used as much of their experience from the LT vz. 35 as possible. The suspension was almost entirely copied from the light tank, aside from a connecting beam between the two bogeys for better rigidity. The idler was the same as on the LT vz. 35. The same four return rollers were also used. As for the turret, it had to be seriously changed from the Skoda S-III design. It received a larger turret bustle. The armament was the same, a 47 mm A9 gun and a coaxial ZB.37 machinegun. Another machinegun was placed in the front of the hull.
The SP-II-b prototype was assembled by Skoda in October of 1937. After factory trials where the tank travelled 1967 kilometers, proving ground tests began, starting on May 5th, 1938. However, the cooperative project met an unexpected competitor even before those trials.
Despite officially cooperating on the medium tank project with Skoda, CKD management had different ideas. The design bureau headed by Aleksei Surin and Karel Exner was working on their own medium tank in parallel with the SP-II-b, indexed V-8-H. The SP-II-b project influenced the V-8-H significantly. Nevertheless, the project picked up a lot of characteristics from previous CKD designs, especially the P-II-b. One can't help but notice the initial turret design, with its characteristic commander's cupola.
The initial project, indexed V-8-He, had its muffler in the rear, like the CKD infantry tank. The suspension was a combination of CKD and Skoda technical solutions. The suspension with nine road wheels and four return rollers was borrowed from the SP-II-b. However, the tank was not a complete copy. The bogeys were new designs, as well as the wheels. The beam connecting the bogeys was used by CKD engineers since the LT vz. 34. The engine was modernized compared to the one on the SP-II-b. The Praha NR's power increased to 241 hp, and it received a new Praga-Wilson planetary transmission.
The experimental prototype of the CKD tank was finished in late December of 1937, and by December 21st, trials had begun in Milovice. The V-8-He differed from its initial project. The hull was even more similar to the SP-II-b, especially the rear. The turret platform retained its similarity to the P-II-b. At the same time as the V-8-He, CKD's design bureau was working on the LTH family of export tanks, elements of which obviously migrated to the project. The V-8-He's commander's cupola is typical for light export tanks. At the time of assembly, the V-8-He turret was not ready, so the experimental chassis held a semi-model with no armament.
Trials in Milovice (near Prague) were a competition between the V-8-H and SP-II-b. Luck was on Surin and Exner's side. The V-8-H successfully passed all trials. In total, the prototype travelled 12,735 km, 5473 km off-road. As for the SP-II-b, it did not work as well. The tank was plagued by technical problems. As a result, the tank was taken off trials and sent for repairs. CKD won.
It's worth noting that the reworked V-8-H underwent a series of changes. According to new specifications, the tank received an improved Skoda A11 47 mm gun. The new gun required a new turret, larger in size. The commander's cupola was altered and moved from the left to the right side. The turret platform had to be changed to accommodate the larger turret. The tank received radio equipment, including a horseshoes antenna, and a set of spare parts. As a result of these changes, the mass grew from 14.7 to 16 tons.
The V-8-H was accepted into service under the index ST vz. 39 (medium tank model 1939). An order for 300 tanks of this type was made on April 20th, 1938. 4 years went by since requirements for category III were issued, but the result was a very modern tank. It had decent armour for the time, adequate armament, and a maximum speed of 45 kph. The ST vz. 39 could fight any medium tank of the era and had room for modernization. The problem was that the tank was born during a very difficult time, which shaped its future.
Despite CKD's victory, Skoda did not leave empty handed. The ST vz. 39 order was spread out so that CKD was only making 95 tanks, the other 205 being produced by their "friends". This was largely caused by CKD's production of the LT vz. 38, as well as foreign orders. According to plans, the first ST vz. 39 tanks were supposed to enter service in June of 1939, and the order would be completed by February of 1940. In reality, the plans kept getting delayed. Meanwhile, Skoda was not sitting still, and a new tank was made in Pilsen using the SP-II-b as the foundation: the S-II-c.
In this convoluted situation, the Czechoslovakian medium tank met the well known events of March of 1939. Czechoslovakia was occupied by Germany. Looking over CKD, the Germans proposed that the LT vz. 38 continued production under the index PzKpfw 38(t). As for the ST vz. 39, it was decided to build one more prototype with a concrete block for a turret. In 1940, trials were performed alongside a German PzIII, as a result of which it was decided to not put the tank into production.
The S-II-c had another fate. The tank underwent trials under the index T-21 in Hungary and Italy. As a result, Hungary obtained a license for the tank on December 6th, 1940. The Hungarian version is known as the Turan.
It's worth mentioning another step in the V-8-H's history. In March of 1939, the Swedish company Svenska Ackumulator AB Jungner signed a contract with CKD for the delivery of 50 light TNH-Sv tanks. Since Czechoslovakia was occupied in March of 1939, the deal fell through. Nevertheless, the Swedes got what they came for, and Scania-Varbis started production of Strv. M/41 light tanks in 1941.
A hitherto unknown fact is that the V-8-H was offered to Sweden alongside the TNH. Thanks to documents from Swedish archives, it is known that CKD sent a large amount of materials regarding the V-8-H. In the fall of 1941, Sweden received a draft project of a new V-8-H, indexed V8H-sv. The main change in this project, dated September 8th, 1941, was a new suspension designed by Aleksei Surin. The large wheeled design, first tried on the AH-IV tankette, proved very good. The front armour of the hull and turret was also increased to 60 mm, and the sides to 40 mm. The tank's mass grew to 20 tons, and top speed dropped to 40 kph.
The project was not needed, as the Swedish AB Lansverk company was already working on the LAGO medium tank, adopted under the index Strv. M/42. The tank, initially classified as a heavy, surpassed the Czech project in every way.