TF-4 (USA, Tier-9, Heavy Flamethrower Tank, techtree)
Historical Reference:
In the early 50s, the four-track design became a very popular idea in NATO countries, and they tried to implement it on the new TF-4 flamethrower tank. The tank was supposed to have very powerful armor protection to successfully operate as a flamethrower machine, and a hydrostatic transmission to ensure high mobility.
A poorly developed development concept led to the TF-4 not even being included in the general list of Question Mark conference questions. As a result, the project got lost among others and did not receive further development. 
