'Air Bomber/NAV II'
This was his rank. In order to serarate the ground NCOs from the NCA of the time, a new rank structure was developed together with new rank badges and independent messes.
The rank had classes plus the aircrew position. (eg Pilot 1; Navigator II etc). Aircrew started as Aircrew Cadet then moved on to Aircrew 1/II (Corporal); Aircrew III (Sgt); Aircrew IV (FS) then Master Aircrew (WO). Only the latter remains in regular RAF - the others were abolished in 1949(?)
ps. If anyone has one of the old NCA rank badges (except Master) the Waddington Heritage centre could do with some examples! Please pm me.