For much of World War II, Germany's most threatening maritime force was the U-boat arm. Their deadly attacks on Allied supply lines are well documented, but they also carried out numerous clandestine operations, landing in neutral countries such as Ireland and Spain, and along the U.S. and Canadian shorelines to conduct espionage and sabotage. North African landings aided Rommel's Afrika Korps. In this fascinating book, U-boat historian Jak Mallmann-Showell...