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