What a great thread!
It is also important to this discussion to remember what was happening at the time this correspondence was taking place. The B.E.F. had just been evacuated from Dunkirk with the loss of most of their heavy weapons and transport (June 1940). The air war that became known as the Battle of Britain was in full fury (July-October 1940) and Operation Seal Lion (sea-born invasion of Great Britain) was awaiting the successful outcome of the Luftwaffe over the Royal Air Force. A very real and imminent threat that there would be a successful German invasion and landing in Britain (hence a need for close in airfield defense) was foremost in the minds of military planners. The Royal Air Force was on its heels and very nearly combat ineffective due to the Luftwaffe bombing attacks on their airfields when the German air campaign shifted to London and giving them much needed breathing room to recover. The rest, as they say, is history and the R.A.F. prevailed over the sky’s of England and Operation Sea Lion was postponed indefinitely.
So my question is, by the time the immediate need for submachine guns had passed, was production and delivery far enough along to make conversion or cancellation impractical or had the military usefulness of submachine guns been proven to make an important part of military doctrine?
As Tom would say, “all good stuff!”