I had this link a while ago but forgot to repost it. This is the war diary of the Commander German Submarines – Italy for the period December 1941, when this post came into existence, to 30 June 1942. It is a postwar translation.

https://archive.org/details/wardiaryofcapta194142germ

There are various forms of the diary at the site, including some more convenient such as Kindle or ePub. Unfortunately these are riddled with errors from the (presumably) OCR process. The PDF is fine, since it consists of pictures of the original translation file. A direct link to the PDF is at this link. I would suggest to rightclick and save, so that you can read it offline. Reading it in your browser is slow and frustrating.