What if Germany followed Donitz's proposals to build a force of 300 U-boats?

[Garrison]

The second S-word... Spain.

Franco does a Mussolini and declares war on Britain and France in June 1940 in the mistaken belief that the war's over bar negotiating the peace treaty.

Francisco (in common with his friend Benito) soon discovers that he's made a mistake of pavarottic proportions. Said mistake is that he's joined a war that's going to continue for years instead of the expected weeks (or at worst months) and not only that he's fighting a country whose substantial navy is between his country and a large part of his food supply, not to mention some other important odds and ends.

However, every cloud has a silver lining which is that Gibraltar instantly becomes untenable as an air and naval base due to its vulnerability to bombardment by Spanish artillery and will be starved into surrendering in a few months which will allow German surface warships to enter the Mediterranean and Italian surface warships to enter the Atlantic.

It's implausible but not impossible.

Sorry but if you want Franco to behave like Mussolini, then yes that is pretty much impossible.

 

[Cryhavoc101]

given the need to replace older ships the RN's heavy ship program would probably be roughly the same as otl if not greater and earlier due to having a larger budget earlier than otl and the 2nd London naval treaty probably not being a thing. The number of sloops and destroyers and other escorts they would build on the other hand yeah that would have gone up a lot

Quite. The ship yards that can build ‘big ticket items’ where far more limited than those who could build escort ships. Britain in 1939 had the greatest ship building capacity of any country in the world and in the face of an obvious threat such as that of Germany building a fleet that capacity would be leveraged to produce large numbers of escort ships earlier than otl.