I'm toying with the idea of a WW2 that opens with a communist France launching an airborne invasion of the UK in the summer of 1939.
Assume that the French achieve strategic surprise - the British didn't see this coming - at all.
What would it take (short of ASBs) for a French victory? How unprepared, relative to historical preparedness at the same point in time (june 1939) would the British have to be?
Are the forces required (in paras and transport aircraft) such that it is an impossibility unless the UK is pacifist and disarmed?
Or would 3 para divisions dropping on airfields Crete style do the trick, if followed up by air ferry of light infantry divisions (like the Nationalist Spanish Morocco to Andalucia air bridge of 1936)? The idea being that their capture would not only open up bridgeheads for air-transportable troops to land but also take out much of fighter command's ability to interfere with the ferrying.
Assume it would take the Reds every transport-capable aircraft they had (including bombers) to lift over the paras, but the bombers would be used as such in subsequent sorties (to make up for the lack of heavy weapons), while the transports ferry troops. Gliders would also be used to increase the number of troops in the first wave.
Eventually, if French control of the airspace over the Channel forces the Royal Navy to pull back, France could move over heavy weapons, such as tanks, and supplies, but early on everything would have to be flown in.