For those interested:
The Diary of a U-boat Commander by Stepehn King Hall (Unknown binding - 288pp in English) was published by Hutchinson & Co in 1920. The ASIN is B00088KONM
U122: The Diary of a U-boat Commander by Karl Von Schenk (Paperback - 136pp) was published by Diggory Press in 2006. The ISBN is 1846850495 and is avaliable from Amazon for $12.99
The Diary of a U-boat Commander by Anonymous with an Introduction and Explanatory Notes by Etienne (Paperback - 142pp) was published by BiblioBazaar in 2006. The ISBN is 1426426755 and is available from Amazon for $10.99
The Diary of a U-boat Commander by Anonymous (Paperback - 144pp) was published by Kessinger Publishing in 2004. The ISBN is 1419159275 and is available from Amazon for $16.35
The Diary of a U-boat Commander - 1920 by Anonymous (Paperback - 308pp) was published by Book Jungle in 2006. The ISBN is 1594623880 and is available from Amazon for $17.45
Amazon also lists a Paperback and Hardcover published in 2003 which sell for $89.99 and $95.99 (a little pricey!)
Another book of this vintage (which I have) is
The Journal of Submarine Commander Von Forstner by Commander Von Forstner, translated by Mrs. Russell Codman published in 1917. The story goes that it was translated into English and published to help stir up hatred for the Germans during WWI, thus to help push the US to declare and enter the war.
Not to forget one of the most well known books of this era,
Raiders of the Deep by Lowell Thomas, first published in 1928.
As you might guess, I collect books on U-boat warfare, the Kriegmarine, The Battle of the Atlantic, etc. Hope this is helpful.