Air-cooled, more than 18-cylinders, multi-row radial engine.

This allowed a smaller engine to produce the same power as a larger one, leading to better fuel efficiency and compact design, particularly in multi-row radial engines.

It is generally difficult to properly arrange pushrods for four-valve operation in a multi-row radial engine, some of the rods would have to exit the crankcase between the cylinders where there is little room or spare strength.