It produced about 375 kW (500 hp), was the first to use gas nitride hardening and introduced wet cylinder liners into Hispano-Suiza's aircraft engine range.

This improved cooling, simplified assembly and allowed larger cylinder bores without increasing their separation.

[2] The 12M and 12N engines were the first to use the gas nitriding surface hardening process on the cylinder walls, which reduced both wear and oil consumption.

They also used a novel, complicated but effective method of main bearing cooling, enhancing the local lubricant flow without requiring high overall oil pump speeds.

Though rather brittle, Elektron metal has only 2/3 the density of aluminium and the result was a 20 kg (44 lb) weight reduction from the 12Mb to the 12Mc.

A final 12M variant, the 12Mdsh run in 1932, addressed this problem differently; it was the first Hispano-Suiza engine to be supercharged, blown by a Rateau turbine.

[3] The Swiss government, in the form of the KTA (Kriegstechnischen Abteilung or War Technical Department) purchased construction licences for the 12Mb and in 1932 sixty units were built at the Schweizerische Lokomotiv- und Maschinenfabrik factory.