Dear Andrey,

Further to my earlier reply, 3 other books based on prime source info which I think would help you are:

Clay Blair's "Hitler's U-Boat War".

Rohwer's "Chronology of the War at Sea".

and

"The Battle of the Atlantic and Signals Intelligence - U-Boat Situations and Trends".

You should be able to find a lot of good and soundly-based information in these.

Yours aye,

Derek.