When the Jumo 211 entered production in the late 1930s it used an unpressurized liquid cooling system based on an "open cycle".

Water was pumped through the engine to keep it cool, but the system operated at atmospheric pressure, or only slightly higher.

The Junkers Motorenwerke firm was not happy with this state of affairs, and started its own efforts to produce a pressurized cooling system as early as 1938.

Experiments on the 211 proved so successful that it became clear that not only could the engine be built smaller and lighter (by reducing the water requirement),[1] but could be run at higher power settings without overheating.

After redesigning the engine block to a smaller external size to suit the increased cooling power – while keeping the same 150 mm x 165 mm bore/stroke figures, maintaining the 35 litre displacement of the Jumo 211 series – and then further increasing boost settings on the supercharger, the resulting 213A model was able to deliver 1,750 PS (metric hp) at 3,250 RPM.

The 213B was designed to run on 100 octane "C3" fuel, allowing the boost pressure to be increased and the take-off power improved to 2,000 PS.

A further substantial upgrade was projected as the 213J, which replaced the earlier model's three valves with a new four-valve-per-cylinder design for increased volumetric efficiency.