The publisher is Spearhead and the title is 7th U-Boat Flottilla Doenitz's Atlantic Wolves by Angus Konstam & Jak Mallman Showell. It's only 96 pages but got loads of photos.
The website for the publisher is
www.ianallansuperstore.com
Yes it was worth it but it was in the sale at a third of the price!
Actually I've just seen it on Amazon.