Dang, I didn't mention the artists who did those covers --
Robert has properly credited J. D. Carrick who illustrated the Harleyford books back in the early '60s.
Mick was illustrated by Peter Endsleigh Castle.
Sopwith Scout 7309 by Pino Dell'Orco.
Over The Battlefronts by Clayton Knight, whose WWI flying experiences are also part of the book.
The Red Baron's Last Flight by Barry Weekly, who's also done the cover art for several other Grub St. titles.