douglas bader recovered from having both legs amputated to become one of britain 's greatest fighter aces .
was shot down over france in 1941 and ended up in german prison camp .
and he was involved in a mass break-out that pre-dated the break in 1944 immortalised in the great escape .
now , hollywood bosses snapped up the rights to turn military historian mark felton 's book about the escape into a blockbuster .