Hello; Large and powerful tractors, weighing more than 20 tons and having more than 600 horsepower, big tractors used to tow heavy loads in different types of agricultural work. The original model was the Challenger 65 featuring the Mobile-Trac System (MTS) consisting of rubber tracks and a suspension system. Although marketed as the world's first rubber-tracked agricultural tractor, a company using surplus equipment inspired by the design of military tanks had produced a considerable anount of rubber tracked tank tractors. The MTS combined the flotation and traction of steel tracks with the versatility of rubber tires. The use of tracks gave the machines increased tractive performance compared to traditional four wheel drive tractors equipped with tires. The Challenger 65 began as a 270 gross HP machine used primarily for heavy tillage. You missed Versatile tractor model 610DT 650HP. then there is the Big Bud 747 which is the most powerful tractor ever made.