It was often squadron by squadron that the new aircraft were introduced. Once a new version of an aircraft was released there wasn’t an immediate replacement of all aircraft of the previous type across the whole air force. If you are really knowledgeable about aircraft you may also be able to identify a squadron by the type of aircraft being used. Squadrons with the same Squadron Code you have can be eliminated. If your ancestor is with a Spitfire then you know he was with Fighter Command and thus the bomber It’s normally relatively easy to tell a fighter aircraft from a bomber which allows you to start distinguishing commands. If you still find there a few too many units, start picking out the equipment visible in the picture. As with all genealogy start feeding in what else you know about the ancestor you are researching and you’ll be able to knock off many units from the list.

units were temporary, forming one year and disbanding the next or were otherwise distinguishable. ‘A’ for example was used 25 times for numerous different units. It is not an infallible system however, Squadron Codes could be and often were repeated. Vickers Wellington long range bombers in flight

Raf squadron codes and serial numbers