The KIA proportion of the U-Boat arm of the Kriegsmarine was 75%.
The US rate was about 20%.
US Air Force losses in Europe were also horrific, but I don't know the percentages.
There’s a superb book to read on the Kriegsmarine’s U-Boat service called “Iron Coffins”. It talked about their 75% KIA rate but the book claims they were never hurting for volunteers.