This is the Trumpeter 00221 kit in 1/35 scale, of the ‘German Schwere Plattformwagen Type SSMYS 80 ton’.
History
During WWII, the SSMYS 80ton vast railroads in Europe and Russia were used to carry military items closer to the front.
In the case of tanks, this got them closer to the battlefield faster than if they had been driven there under their own power. It also left the tank crews fresher for battle.
This particular SSYMS 80 ton, was used for carrying the Germany Panther and Tiger heavy tank.
Source: Trumpeter website