Chieftain tank
Simpkin was commissioned into the Royal Tank Regiment in 1941. He cut short a degree course at the University of Cambridge to do so. He served in North Africa where he won the Military Cross and was taken prisoner. Simpkin was awarded an Order of the British Empire (OBE) for his part in the new design of the Chieftain tank and retired from the army in 1971. He continued to write, lecture and consult about armor doctrine, tactics and Soviet thinking, living at first in Norfolk, England where he was brought up and then in Elgin, Scotland.