http://en.wikipedia.org/wiki/German_submarine_U-3519
http://en.wikipedia.org/wiki/Type_XXI_submarine
Between 1943 and 1945, 118 boats were assembled by Blohm & Voss of Hamburg, AG Weser of Bremen, and F. Schichau of Danzig. Each hull was constructed from eight prefabricated sections with final assembly at the shipyards. This new method could have pushed construction time below six months per vessel, but in practice all the assembled U-boats were plagued with severe quality problems that required extensive post-production work to rectify. One of the reasons for these shortcomings was that sections were made by companies having little experience in shipbuilding, following a decision by Albert Speer. As a result, of 118 Type XXIs completed, only four were fit for combat before the Second World War ended in Europe.[5]
It was planned that final assembly of Type XXI boats would eventually be carried out in the Valentin submarine pens, a massive, bomb–hardened concrete bunker built at the small port of Farge, near Bremen.[6] Construction took place between 1943 and 1945, using around 10,000 concentration camp prisoners and prisoners of war as forced labour.[7] The facility was 90% completed when, in March 1945, it was badly damaged by Allied bombing with Grand Slam “earthquake” bombs and abandoned. A few weeks later, the area was captured by the British Army.[8]
Interesting about the Type XXI submarines. The component construction doesn’t sound like a bad idea. I’m also not sure how much the relative inexperience of the German firms contracted to build sections affected the end product. Knowing how much building a submarine is a very exacting craft, I would think that the labor force, both in the components and final assembly, is probably key to whether the Germans were making good submarines or not.
So a labor force of concentration camp inmates, Russian POWs and slave laborers, who don’t know dick about the technology, and who really don’t want to see Germany win the war, isn’t a labor force that’s going to build good submarines. Once you’re working with that, it doesn’t really matter how good your blueprints are.