Heavy tractor M1, caterpillar D7 : ordnance maintenance - USA Voorschrift, Technical Manual, 9-1773 Tractor, Crawler, Diesel, 70 to 90-DBHP, Standard, Caterpillar D7, 74-In. Gage, with La Plant-Choate R-76R, Angledozer and Le Tourneau R-7, Power Control Unit. (Serial Nos. … Tractor, Crawler, Diesel, 70 to 90-DBHP, Standard, Caterpillar D7, 74-In. Gage, with La Plant-Choate R-71, Angledozer and Le Tourneau R-7, Power Control Unit. Serial Nos. …