U-Boats Against Canada: German Submarines in Canadian Waters - Michael L. Hadley - Google Books

https://books.google.de/books?id=LJJez91DyYcC&pg=

The U-boats constituted a serious threat to North American security and a major challenge to coastal and convoy defence. Hadley reveals the military and political impact on Canada of in-shore submarine warfare and vibrantly documents the successful German…