In 1939, the era of the red Case tractors began. Significant steps were also taken in the design, including a curved grille in front of the radiator. The C model was replaced by the D, and the CC by the DC. The engine power was mainly increased by raising the engine speed. Both gasoline and kerosene versions were available. The number of gears was increased to four, so the highest gear was already sufficient for highway driving, since the maximum engine speed was 1550 rpm. The brakes were now oil-bath disc brakes, and power steering brakes were available as an option. In 1950, hydraulics were introduced in the D series, and in 1952 a lift equipped with a draft control system and a liquefied petroleum gas version were introduced. Both the hydraulics and the power take-off were independent of the clutch.

A year later, an updated version of the L model, the LA, was introduced. The engine's compression ratio was raised, and lubrication improved. There were four gears as standard, and the electrical system was available for an additional cost. Fuel options included kerosene, gasoline, and liquefied petroleum gas.

In 1941, the S model and its row-crop version SC were introduced below the D in the lineup. These replaced the R model, which had an outsourced engine. The new engine was 2.5 liters and primarily a gasoline version. This model also had four gears. The 1953 models featured an enlarged 2.7-liter engine.

There are quite significant differences in the reported power ratings. The LA model's power as a gasoline version was 55 hp both in the USA and in Finland. In Finland, the S-ex model was rated at 30 hp for the gasoline version and 27 hp for the kerosene version. For the D-ex, correspondingly, 40 hp and 37 hp. The export market ex-versions included, among other things, power steering brakes and a padded seat.

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