The Royal Air Force also formed 15 commando units in 1942, each of which was 150 strong. These units consisted of trained technicians, armourers and maintainers who had volunteered to undertake the commando course. These RAF commandos accompanied the Allied invasion forces in all theatres; their main role was to allow the forward operation of friendly fighters by servicing and arming them from captured air fields. However, due to the forward position of these airfields, the Royal Air Force Commandos were also trained to secure and make safe these airfields and to help defend them from enemy counterattack.