One of the topics that I've always thought was interesting, but never got around to learning about in any detail was the U-Boat campaigns in World War 1. Despite the glamour of the Wolfpacks and the Battle for the Atlantic, it seems that the first act of the U-boat war was more successful for the Germans, and actually endangered the British war effort to an extent the Nazis wished they could do in World War 2. Then there's the whole Lusitania affair, the Unrestricted Warfare campaign, and the eventual entrance of the Americans into the fray on top of all that.
So from what I've found...
(1) There isn't much in the way of English sources on the U-Boats. I'm reading The U-Boat War 1914-18 by Edwyn Grey, and despite being almost 50 years old, it seems to be the most popular book on the topic. Please tell me there's something better out there. Not that it's bad, but it seems to establish a lot of the stereotypes that people think of the war.
(2) The British had a much larger U-Boat force, but what did it actually do with it? I have a book on my wishlist that covers the British submarines in the war, but does anyone have any good websites on offer?
(3) The Big Question: How close did the Germans get to knocking out the British with their U-Boats?