exhaust-driven supercharger

A turbocharger is an exhaust-driven supercharger (fan or blower) which forces air into the engine under pressure.

These engines had their exhaust-driven supercharger (a concept nowadays known as turbocharger) mounted on the nose under the propeller, with much exposed pipework.

The U.S. Army Air Corp's P-39 and Curtiss P-40, which used the same engine, had the same difficulty; the Lockheed P-38 Lightning used the same engines but incorporated exhaust-driven superchargers to achieve good altitude performance.