The Diary of a U-Boat Commander (1918) by Stephen King-Hall purports to be the account of an actual German officer during WWI. It is a vivid glimpse into one man's experience from the start of his position on a U-boat (Unterseeboot), fighting during an intense submarine blockade, and his passionate longing for a sweetheart back home in Germany. In the beginning, Herr Shenk is a stereotypically arrogant Prussian nobleman, disrespectful of his inferiors. Eventually comes to a deep understanding the evils of war and the maniacal order he served.
Readers won't like Shenk at first, but read on! The story (true? made up?) gets going during the second half: Herr Commander makes decisions which will impact the lives of crew and country, but will ultimately wrestle with his own soul in the face of conflict. Anyone interested in the Great War, especially its vicious sea-battles, will enjoy this diary of a U-Boat commander who undergoes a monumental change of heart.