The Challenger was the result of several development programs over a long period of time. The program started in the 1970s and involved both D6 based units and Grader power units. A parallel program was also developing wheeled high hp tractors based on using the articulated loading shovel chassis units. The was latter merged with the crawler team after a few years. The result was the Challenger Tractor and the "Mobi-Trac" system.