This post cites a much better article by Marcus Jones on the boat and the context in which the boat was developed: http://www.usnwc.edu/getattachment/dd165021-2

This post cites a much better article by Marcus Jones on the boat and the context in which the boat was developed: http://www.usnwc.edu/getattachment/dd165021-2812-40ba-847f-d5b4c3e4ac4e/Innovation-for-Its-Own-Sake--The-Type-XXI-U-boat.aspx http://www.usnwc.edu/getattachment/dd165021-2812-40ba-847f-d... Jones's article is better in the sense that it is more reasoned and without single-paragraph overstatements like "But everything about the Type XXI was a mistake." It also, unfortunately, takes more effort to parse. Jones's article also has different take: "...this paper argues that the U-boat Type XXI was nonetheless not nearly so unrealistic a solution as [Tooze's] account suggests...", and also suggests that while the Type XXI was an evolutionary solution, it's accelerated development was revolutionary.