The Allis-Chalmers D21, introduced in 1963, was a landmark model in the company's lineup, being the first Allis-Chalmers tractor to offer over 100 horsepower. The Series I D21 was equipped with a naturally aspirated, six-cylinder diesel engine that produced around 103 horsepower, making it one of the most powerful tractors available at the time. This model featured a rugged design and robust construction, capable of handling heavy-duty agricultural tasks such as plowing large fields and pulling heavy loads. The D21 also included the innovative Power Director transmission, which allowed for seamless shifting and improved control, enhancing its efficiency and ease of use on the farm.
In 1965, Allis-Chalmers introduced the Series II D21, which brought significant advancements, most notably the addition of a turbocharged engine. The turbocharged diesel engine boosted the tractor's power output to approximately 125 horsepower, making it even more capable of handling demanding agricultural tasks. This increase in power and performance solidified the D21's reputation as a top-tier tractor for large-scale farming operations. The Series II also featured improved hydraulics and operator comfort, ensuring that farmers could work efficiently and comfortably for extended periods. Today, the Allis-Chalmers D21 is celebrated by vintage tractor enthusiasts for its groundbreaking design and significant contributions to the advancement of agricultural machinery.