Tony Zbaraschuk posted an interesting link to the Lois McMaster Bujold Mailing list (http://lists.herald.co.uk/cgi-bin/mailman/listinfo/lois-bujold):
Design Studies of German Submarines by the US Navy
The Design Study of Type IXC U-boats was made available by Scott Sorenson. The Design Study of Type XXI U-boats was made available by the Portsmouth Naval Shipyard Public Affairs Office and the Navy Yard Museum — in particular Debora White, Gary Hildreth, Jim Dolf and Bill Tebo (a member of the US Navy crew of U-2513).
Photographs and documents of surrendered German submarines and their crews were made available by John Cunningham (a member of the US Navy crew of U-2513).