The Allis-Chalmers Model B, introduced in 1937, was the first modern tractor available for under 500 dollars. The Model B was designed to pull a single-bottom plow, replacing the horse. Its appearance, with its rounded lines, differed significantly from earlier A-C tractors. The tractor's frame was very narrow in construction. It was designed for rubber tires, but during the war, many were equipped with steel wheels. The engine was A-C's 1.9-liter four-cylinder gasoline engine. Power from the belt pulley was 16 horsepower. There were three forward gears. Optional equipment included a hydraulic lift, electric start, and from 1945 onward, an adjustable front axle track width. The Model B did not have the traditional belt pulley on the side of the tractor as standard; instead, it was attached to the power take-off shaft at the rear when needed. The early B models featured steering brakes operated by hand levers.

A combine harvester, the All-Crop Model 40, was customized for the Model B and also became popular.

The Model B was also assembled in Britain from 1947 to 1949. In total, about 120,000 units were sold.

In 1941, the Model C was introduced, which was very similar to the B but sized for a two-bottom plow.

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