The Pobjoy P was a British seven-cylinder, air-cooled, aircraft engine designed by Douglas Rudolf Pobjoy and built by Pobjoy Airmotors.
It became the progenitor of the Pobjoy R/Niagara/Cataract family of small radial engines.
A notable feature of the Pobjoy P was the propeller reduction gear which allowed the small engine to operate at more desirable higher speeds.
[1] Data from Jane's all the World's Aircraft 1928[2]