I have a 1917 book that describes the exploits of a German submarine between 12 and 30 April 1916. It's — naturally — propaganda (though my copy is a Dutch translation published in Amsterdam) to show how well the submarine service was doing, but interesting reading nonetheless. The title translates as "War diary of U 202" by Kapitänleutnant Freiherr Spiegel von und zu Peckelsheim, but the afterword indicates that "U 202" is a fictional number to hide that of the real boat.