Hi, I hope I can help a bit.
I don’t think you will ever know for sure what he was wearing as a number of different watches were in service at this time
However to narrow it down a bit when did he get his wings and what did he fly? The date he got his wings might narrow down the watch type he would likely have been issued, the type of aircraft he flew could help determine if he would have had a Chronograph or time only watch.
One thing is certain however if he wore an issued watch whilst flying it would be marked 6B or 6BB for RAF not W10 for Army.
Possible answers could include:
Hamilton Chronograph
Hamilton 6B
Hamilton 6BB
Smiths 6B
Omega 53 (if re-issued to him)
IWC MK11 (if re issued to him)
Lemania single and double button Chronographs
The sterile 6B (Although these were 76 issue I think)