The historic Caterpillar D2, was first produced in 1938 and was the smallest diesel-powered track-type tractor available on the market.
Caterpillar began producing this model (among others) in response to the "New Deal" programs that were initiated by President Franklin D. Roosevelt to stimulate America's economy during the Great Depression.
Check out this customer story from 1938, featuring farmers Herbert and Arthur Jesswein.