There are plenty about it depends what you want you have books like:
German submarine warfare world war I Lawrence Sondhaus
The U boat war Edwyn Grey
K boats by Don Everett
British submarines of world war one Innes Mc cartney
What sort of books are you looking for cause i could probably list all day
technical Information
Stories of missions
Campaign doctrines
If you want a unique one Lesrae (Les Robertson) on facebook did upload his friends relatives world war one diary he transcribed it and its now available.
Diary of captain Pearson
https://www.dropbox.com/s/7gizvon4gv...%20RN.pdf?dl=0