Besides Ken Dunn's thorough, excellently researched, and well-reasoned article, most U-boat officers (especially in the first half of the War when they were most active) were ex-merchant seamen. Over and over again, you read of them expressing opinions like "we regret any loss of life; they're sailors just like we are -- but it's necessary in war to sink the ship" and "we'll give them all the help we can, we're all sailors on the sea" (these were statements circulated among the U-boat men, reinforcing their stated standards, as well as comments made to survivors in lifeboats). And as Ken's article points out, there was strong leadership from Doenitz as to standards of conduct for U-boat men -- not only did Doenitz stand up to Hitler at his own peril on the treatment of survivors, his conduct was such that even the most thinly arrayed "war criminal" charges after the War could not be substantiated against him.