Your "what ifs" tend to differ from other peoples.
Yours tend to need time travel. As in develop engines or aircraft several years before they became available. Or fuel or........?
Other people are asking what could have been done with existing knowledge and resources if applied in a different way.
For example the British lost a fair number of airplanes due to using crappy propellers. Losing an engine on an overloaded bomber often meant the loss of the plane when you were using two pitch props or even constant speed props. The British were not only late in fitting constant speed props but almost criminally late in fitting fully feathering props, which while not a guarantee of returning with a single engine improve the single ceiling by thousands of feet due to lower drag of the prop and less drag due to trim changes.
Fully feathering propellers were in use by 20 different airlines around the world in 1938. Why the British were fitting two pitch props to combat planes in 1940 has never been really explained. It doesn't require much to ask what would better propellers, which existed in a number of other countries and were available for licence (companies were actively seeking foreign companies to licence their product), have done for both performance and loss rates of British planes in 1939-41.
The British didn't need Lancasters in 1939/40 for anti sub patrol (Spitfires sure weren't going to do it) and the Avro Anson was not up to the task by any stretch of the imagination even though it was used. There was no "Atlantic Gap" in 1939-40 because many of the German subs could NOT reach the mid Atlantic stay for even 2-3 days and make it home without running out of fuel. Lockheed Hudsons and Blenheims (created by changing Botha production?) would have increased Coastal commands effectiveness quite a bit over many of the planes actually used at this time. 12-16 Catalinas would have made a considerable difference, as some of the British flying boat squadrons only had 6-8 planes.
Sunderlands are great but you don't need a Sunderland to get a more effective plane than this
Equipped two squadrons in Scotland and one at Gibraltar at the start of the war.
I'm still trying to figure out why the RAF didn't use constant-speed props sooner. It is, as far as I can tell, one of life's great mysteries. As an aside, Dehavilland was a licensee for Hamilton Standard from the mid-1930s and remained so until its demise.
Anti-submarine patrol aircraft have some effect even if they have
no armament, as long as some of them do: a submarine on the surface cannot safely assume that the aircraft coming at it out of the sun is armed or not, and it doesn't take much to make it unsafe for a submarine to submerge. Since the RAF had air-surface radar by 1940, a very high priority should be putting it onto any maritime patrol aircraft large enough to carry it. I'd also consider producing land planes for the anti-submarine role to be a high priority. Some of these could be aircraft without the performance to operate over the Continent or where Luftwaffe fighters could operate -- there weren't going to be many Luftwaffe aircraft operating west of the British Isles -- but some should have the performance needed to operate in more dangerous environments. Lancasters would have been great (although a copilot would have been nice on those long, hopefully boring night time over water flights) but Halifaxes would also serve (their poorer high-altitude performance wouldn't be problematic), as may Sterlings (same logic). Figuring out a reliable way to put holes in a surfaced U-boat's hull would be a nice touch. You're right: Ansons wouldn't do it. Blenheims and Beauforts might, but there's no necessity for seaplanes for this role. While I love seaplanes (and I think they had a very real role at the time), the RAF had places to base land-based maritime aircraft, and the only shortcoming of land-based aircraft in this role is that they couldn't alight and rescue people. Considering that seaplanes (floatplanes even more so) are severely limited in how rough the water they land and take-off from can be, this should not be a major consideration for ASW patrol. That Halifax or Blenheim or Beaufort could take off from land in the sort of weather where a Sunderland can't take off from the water.
Here's my logic:
- Submarines of the era are severely constrained in mobility and range if they're forced to submerge.
- A submarine commander cannot assume an aircraft isn't armed, so must submerge at any contact.
- If the submarine commander doesn't submerge, even minor damage is a mission kill.
- Forcing longer routes to avoid aircraft constrains time on station
Of course, pre-war, the assumption was made that France, the Netherlands, Norway, Denmark, and Belgium would not be available for submarine bases. Since, of these countries, only France had a significant chance of stopping Germany without a great deal of outside help, a bit of diplomacy may be useful here. British diplomacy between the wars was largely enabling of German expansionism as the UK permitted German violations of the naval terms of the Treaty of Versailles. Hitler would have violated it in any case, but the Anglo-German Naval Treaty poisoned UK-France relations with no benefit to the British. So, how does British diplomacy help make these countries strong enough to resist German invasion? Obviously, the penurious defense budgets of Belgium and the Netherlands didn't help.