German Submarine War by Gibson & Prendergast. Post WWI history. Classic.
reprint available. Most of it is available free at googlebooks

Four Years of Underwater Cruising by Johannes Spiess. Weddigen's watch officer. Later became Uboat commander. Present at the mutinies. English Translation by Hyman Rickover.

Diary of A U-Boat Commander. by anon. Awful book which I think is a propaganda piece but has enough detail to be based on reality. Available free at gutenburg project.

U-Boat Westwards! Ernest Hashagen Campaign in 1917

U-boat Stories by Claus Bergen. Post war book. Propaganda type with exploits of German Submariners. Claus Bergen was a naval artist who accompanied uboats on patrols.

Raiders of the Deep. Lowell Thomas. As above but by an Amerian.


Remainder or in German or tranlsated into French or Spanish or Italian. Not English.

There is another on the merchant u-boat Deutschland. I think it is titles Merchant Uboat by the submarine commander. Published during the war. Never read it. Available from USNI.