Widely unknown, the Soviet Union received some 7,500 track-laying tractors through Lend-Lease during WW2, the three main producers being Caterpillar, International and Allis-Chalmers.
While the bulk of the crawlers were of the light and medium type, over 1,000 were heavies.
Among the latter were 243 D-7 produced by Caterpillar during 1942 and 1943, the balance being the Allis-Chalmers HD-10W and the IHC TD-18.
Caterpillar produced 453 Medium Tractor M1 as well, the D-6, very similar in appearance to the D-7 and best recognizable by the different position of exhaust pipe and air cleaner.
The Red Army instantly deployed both of them to their heavy artillery units where they excelled mainly as prime movers, e.g. during the fierce Carpathian mountain fightings of 1944 displayed by the first photography (bottom right).

Special thanks to Mr. Michael Franz, Germany and Mr. Alain Dupouy, France, for providing precious informations.