In the early 1930s Rolls started planning for the future of its
aero engine development programs, and eventually settled on
having two basic designs. The 700 horsepower Peregrine was an
updated development of their existing V-12 Kestrel which had
been used to great success in a number of 1930's designs. Two
Peregrines bolted together on a common crankshaft into an X-24
layout would create the 1,700hp Vulture, for use in larger
planes like bombers. There was also the possibility that the
famous R engine from the Supermarine racing planes could be
developed into a 1,500hp class engine of its own, itself a
development of the Buzzard, a scaled up Kestrel. However this
plan left a large gap between 700hp and 1,500hp. To fill the gap
work was started on a new 1,100hp class design as the PV-12 – PV
for "private venture" as they received no money for work on the
project. It first flew on the front of a Hawker Hart biplane in
1935, using the new evaporative cooling system then in vogue.
The cooling system proved to be