The first prototype engine ran on 24 April 1939, and was later air-tested on the nose-engine mount of a Ju 52. Production called for two primary models, the 222A and 222B, which differed only in the direction that they spun, intended to be used for left-hand (portside wing) and right-hand (starboard wing) engines on twin-engine designs. However, continued testing went poorly, and Junkers eventually decided it was best to stop development of these "Series I" engines and move onto a modified "Series II". The new 222A-2 and B-2 ran at a slightly slower rpm but had slightly larger cylinders of bore (49.88 litres, 3043.86 in³) for the same net performance, while the A-3 and B-3 used a different supercharger for better performance at higher altitudes. One A-3 and B-3 powerplant each were allegedly fitted to the ninth Junkers Ju 288 prototype airframe for flight tests. Both "uprated" models of the Jumo 222A/B versions continued to prove unreliable, and were fitted only experimentally.
