The Gray tractor has its origins in the orchard tractor developed by the New York fruit grower, W. Chandler Knapp. Knapp marketed his two-cylinder design as the Knapp Farm Locomotive, which was notable for its two rear drive wheels that were joined together to improve traction. Further modifications saw the use of a four-cylinder Waukesha engine and the replacement of the two rear drive wheels with a single fully-enclosed drum that was driven by a chain. Chandler Knapp's company was bought by the Gray Tractor Manufacturing Co. in 1914 and the "drum-drive" tractor was renamed the Gray Model A 20-35 tractor. Several years later, the smaller Model B 15-25 was added to the lineup. The year 1917 saw the company renamed as the Gray Tractor Co., and this coincided with the introduction of the 18-36 model, which was built until 1922 and was probably the most popular tractor produced by the company. Other models were also introduced in the 1920s, including the 22-40 "Canadian Special", but the design was starting to show its age and the company ceased tractor production in the early 1930s.

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