RAF Aircrew watches.

Can anyone help me on this one? Am looking for info on these watches. I know that there was a 6b/159 pilots watch that was issued from 1936 to 1941 when this was replaced by the 6b/234 which had a 'hack' function on the watch. I have been told that both these watches were for Aircrew/Pilots (Prodgers book also confirms this) but some dealers have told me that the 6b/234 was for Groundcrew and Observers only - which is correct?
Also most of these watches were from Omega, Longines Jager le Coulture, Movado, IWC and Zenith but I have found a 6b/234 with the AM stamp and Kings Crown on it but made by Optima - has anyone heard of this company?

Nigel Carver
O/C RAF at War