NigG (your #50),
...that one factor may have been his rank... he was an acting Sqn Ldr, substantive Flt Lt. He might have needed to be a substantive Sqn Ldr to be awarded a DSO (unless he'd shown extraordinary valour)...
He would've been a
War Substantive Flt.Lt.
Smith has a Wg Cdr J.D.Gibbs in the Index, (in the Acknowledgements he has him as "Dennis Gibbs") as commanding 82 Squadron. I think we are talking about a Wg Cdr D.R. Gibbs, DSO. He won his on a Blenheim Squadron, which had been having a hard time doing shipping sweeps and the like in the Channel. So heavy were the losses that he (a mere F/O, or even a P/O) found himself commanding the Squadron (as the senior officer left alive). He did a very good job (as an Actg Wg Cdr. ?) and got the DSO for it. Or so the story went. He was certainly out in India in my time.
So I don't think (if the story be true) that your Dad was a War Sub Flt Lt. would have been a bar to a DSO award. Far more likely is the discreditable fact that the RAF top brass were bent on talking-down the Vengeance (in particular, and dive bombers in general), with the intention of talking them out altogether; restricting awards would fit in with that. Smith has a lot to say about it.
...So perhaps he felt the chaps flying over Burma had had it relatively easy...
Some of the chaps had it easy ! - the VVs. The Jap Army Commanders in Burma seemed fixed on the idea that their Oscars were supplied for Army Co-Op duty only, and never thought of turning them loose on us. Most of the late 1942 VV pilot intake were straight off a Fighter OTU; but any fool could see that a properly handled pair of Oscars could destroy a whole box-of-six VVs without difficulty (if we stuck together, which was the tactic).
100 m.p.h. faster than a VV, infinitely more agile and more heavily armed, they'd cut us to ribbons. We had to fly with this Sword of Damocles hanging over us all the time, but thankfully it never fell !
Preview: one of the first fruits of my research: the Le-u problem is solved. 84 were at Khumbirgram, not in the Arakan. Khumbirgram to Le-u is only 130-odd miles. A VV could do it easily. The D.Tel. has a lot to answer for.
Danny.