OK, a few responses.
The U-boats arent going to spend their entire time submerged. Charging with the schnorkel (especially the early versions) was not easy, it resulted in a lot of 'gasping' as the air cut off, on, off, on. You can probably get them to stay submerged in Biscay (after the aircraft start taking a toll), but I see it was very unlikely in mid atlantic. They dont know about centimetric radar, remember.
IN any case, any sort of issue or problem is going to make them want or need to surface, so they will still lose some boats to air attacks - not as many, though.
Squid isnt obsolete - if it was, the RN wouldnt have spent the time and money postwar developing Limbo to use against these sorts of boats.
Its better if you have a faster escort, and its better when you have more than one escort,but it will still happily sink elektroboots.
The homing torpedo was slow to reduce noise issues at speed, and probably to make it lighter too. Quite easy to get the speed up when intel shows Germany is developing a fast U-boat. It simply wasnt needed OTL
You cant use the pressure hull from the 9 for the 21, they were quite different sizes and shapes. You need to develop a new hull from scratch. Tank tests have limited use (they werent that sophisticated at the time), and in particular the analysis is slow, so it takes a long time. This isnt such a big deal normally (as you are rarely looking at a radicaly different hull design), but this time you are.
I was being generous to the Germans both for development times and build times.
Based on displacement (remember, no fancy electronics in WW2 ships, so there is a very close tie in between displacement and cost) the 21 will cost around 60% more than the 9. So thats either a lot more resources, or fewer boats.
I'm confused that convoys werent the U-boats main targets?? Precisely what were they doing in mid-atlantic then???
The high uw speed helps reaquisition a bit, but not that much - remember, they are only about as fast as they were OTL on the surface, and denial of reaquiring works pretty well then.
While the 21 is a better uw boat than the 7 or 9, I'm rather unconvinced its a miracle war winner. Indeed, looking at resources, numbers, and so on its possible to argue it would be LESS damaging to the convoys than in OTL.
Given the limitations of WW2 tech, there are certain advantages in numbers.
My personal feeling is that it would result in more sinkings at first, that the British will certainly be aware its coming (and I see no way its there before 1941 at the earliest, and late 41 is I think more realistic), resulting in faster development of some weapon systems, and taking a bit longer to grind the u-boat campaign to a halt, but its not going to have a huge effect on the war by that time.
The U-boats arent going to spend their entire time submerged. Charging with the schnorkel (especially the early versions) was not easy, it resulted in a lot of 'gasping' as the air cut off, on, off, on. You can probably get them to stay submerged in Biscay (after the aircraft start taking a toll), but I see it was very unlikely in mid atlantic. They dont know about centimetric radar, remember.
IN any case, any sort of issue or problem is going to make them want or need to surface, so they will still lose some boats to air attacks - not as many, though.
Squid isnt obsolete - if it was, the RN wouldnt have spent the time and money postwar developing Limbo to use against these sorts of boats.
Its better if you have a faster escort, and its better when you have more than one escort,but it will still happily sink elektroboots.
The homing torpedo was slow to reduce noise issues at speed, and probably to make it lighter too. Quite easy to get the speed up when intel shows Germany is developing a fast U-boat. It simply wasnt needed OTL
You cant use the pressure hull from the 9 for the 21, they were quite different sizes and shapes. You need to develop a new hull from scratch. Tank tests have limited use (they werent that sophisticated at the time), and in particular the analysis is slow, so it takes a long time. This isnt such a big deal normally (as you are rarely looking at a radicaly different hull design), but this time you are.
I was being generous to the Germans both for development times and build times.
Based on displacement (remember, no fancy electronics in WW2 ships, so there is a very close tie in between displacement and cost) the 21 will cost around 60% more than the 9. So thats either a lot more resources, or fewer boats.
I'm confused that convoys werent the U-boats main targets?? Precisely what were they doing in mid-atlantic then???
The high uw speed helps reaquisition a bit, but not that much - remember, they are only about as fast as they were OTL on the surface, and denial of reaquiring works pretty well then.
While the 21 is a better uw boat than the 7 or 9, I'm rather unconvinced its a miracle war winner. Indeed, looking at resources, numbers, and so on its possible to argue it would be LESS damaging to the convoys than in OTL.
Given the limitations of WW2 tech, there are certain advantages in numbers.
My personal feeling is that it would result in more sinkings at first, that the British will certainly be aware its coming (and I see no way its there before 1941 at the earliest, and late 41 is I think more realistic), resulting in faster development of some weapon systems, and taking a bit longer to grind the u-boat campaign to a halt, but its not going to have a huge effect on the war by that time.