The most widely used of Junkers' series of six-cylinder inline four-stroke aircraft engines was the L5, first run in 1922.

This engine was used in 1927 as the basis of the 665 hp L55, which had two banks of six cylinders aligned at 60°.

These banks had the same bore, stroke, camshaft operated twin pairs of valves per cylinder, watercooling etc.

A supercharger was added after a year to improve high altitude power.

The high altitude research Junkers Ju 49 may have used the L55 at the start of its flight programme.