The Allis-Chalmers HD-11 tractor: an overview by Richard Campbell Designed as a replacement for an earlier tractor, the Allis-Chalmers HD-11 was a very worthy successor and was in production for over 25 years. By Richard Campbell THE ALLIS-CHALMERS model HD-11 was introduced in 1955 as a replacement for the company’s model HD-9, which had been in production since 1950, and the earlier model HD-10, the 10-year production run of which began in 1940. Both the HD-9 and HD-10 were powered by 71 serie