I posted the below response to the post by
@Tyr Anazasi in the Fandom AH forum. Then I thought that this would be a better fit in Post 1900 since I don't think any of these are actually ASB. The intent is assess which of these is the craziest idea, and provide a list from craziest to least crazy.
Why are the German plans of Operation Seelöwe and H-44 are considered insane. In regards to the Baltic Project and Habakkuk they were somehow realistic. Especially as H-44 type BB was only a study, never intended to be built.
I do not know the actual reasons, but here is my speculation. Sea Lion at its most basic level was a reasonable concept. If you want to get a nation to surrender, you generally have to invade it. However, amphibious invasions of a country with a much bigger navy are problematic. There are whole threads that go into detail as to why Sea Lion could not have worked given the forces available. There are multiple threads in Post 1900 discussing it in more detail.
As for the H-44 type battleships, granted they were only design studies, but design studies for ships that could not have been built given existing shipyards is a little bit crazy. It was even crazier given the waste of engineering effort the design study represented, since the ships could not have been built and the guns didn't exist.
On the other hand, all the references I have heard about the Baltic Project indicate that it was crazy too, although slightly more feasible than Sea Lion since it was a case of the biggest navy invading the territory of the second biggest navy instead of Sea Lion which had the 6th biggest navy trying to invade the second biggest navy. As I understand it, the Baltic Project involved an amphibious invasion of the German Baltic coast north of Berlin.
Given the British had the biggest navy, it doesn't seem technically impossible to land 50,000-100,000 troops on that coast. They would have to get a lot of ships together, build specialized vessels, and escort them and clear the mine fields, but it was technically feasible. However, it would provide the Germans with a target rich environment and the possibility of defeating the Grand fleet in detail, which would cost the Allies the war. Hence, it was a crazy idea and never taken seriously except by Fisher and maybe Churchill.
As for Habbakuk, it was intended to deal with a real problem, the lack of air cover in the mid-Atlantic, the so called "Black hole of the Atlantic". U-boats were significantly less effective against ships with aircraft overhead because the aircraft could spot them on the surface, which meant they had to spend more time submerged. Underwater, they could not catch a convoy and were ineffective unless the convoy was headed right at them. Fleet carriers were one way of providing aircover, but the loss of HMS Courageous in 1939 meant that navies were reluctant to risk them.
Habbakuk was meant to be a large carrier that could operate indefinitely in the North Atlantic and was effectively immune to torpedoes, so it could not be sunk, unless HMS Courageous. It was to be built with ice made of water and woodpulp to improve its strength. Refrigeration machinery would keep it intact as long as it stayed in the North Atlantic and podded engines meant it could lose one or two and keep moving (slowly). They even built some models and a prototype, but itr was overtaken by events, specifically the introduction of escort carriers and long range maritime patrol aircraft to ensure convoys could have continuous air cover.
Habbakuk was a technical feasible response to a real problem, but was overtaken by other solutions. If the technology had been available earlier, it probably would have been built and used successfully, so I don't think it was crazy. Outlandish and unusual, yes, crazy no. Granted, it should have been cancelled faster once the escort carriers became available, and its continuation into 1944 was crazy, but the basic idea wasn't.
All in all, I would say that H-44 was crazier than Habbakuk because H-44 could not be built and Habbakuk could. H-44 was a paper study that wasted design engineer time for something that could not be done and had not real purpose anyway beyond satisfying Hitler's ego. Habbakuk was a real attempt at solving a real problem that could have been built and would have furthered the Allied war effort, but was properly abandoned when it was overtaken by other solutions (although it should have been cancelled faster).
Sea Lion, unlike H-44, did have a valid military purpose, and could have been tried. There are lots of threads that go into detail about why it would not have worked. I don't have time to repeat them here. The Baltic Project was also nuts, but in a different way. It was less necessary than Sea Lion (to force an island power to concede defeat, you have to cross the surrounding body of water), since Germany is not an island. However, given the size differential between the Grand Fleet and the High Seas fleet, it wasn't at least immediately ridiculous, the way the size differential between the Kriegsmarine and the Home Fleet made Sea Lion look immediately impractical.
I haven't seen any books or articles, or threads here, that go into detail why the Baltic Project was crazy. I would expect that they just point out that it exposes the Grand Fleet to the risk of serious attrition from mines and torpedoes, that could cost it enough ships that it could not beat the High Seas Fleet in a fleet action. Once that happens, Britain and the allies have probably lost the war.
In summary, I would assess these ideas in order of craziness from most to least as follows:
H-44 - craziest because it was technically impossible and operationally pointless.
Sea Lion - pretty crazy because while it met a strategic need (compel the UK's defeat) it had a host of technical problems.
Baltic Project - pretty crazy as well, although perhaps a little less so. It probably had fewer technical issues, but a poorer strategic justification in that there were other ways to defeat Germany (invasion over land, for example). I would be interested in any books, articles, or threads that discuss the Baltic Project in detail and why it was a crazy idea.
Habbakuk - not that crazy in concept and met a real operation need, but overtaken by other solutions. In the unlikely event that I ever try my hand at a alt-WW2 TL, I might try to envison the consequences of having the Habbakuk technology available earlier, say if some millionaire had come up with the idea of building one as a refueling stop for high-speed (faster than flying boat) airliners in the mid-30s.