I've tried to compile some data on the first year of combat operations for the u-boats, defined as September 1st 1939 to August 31st 1940. I've used a list of patrols from the first volume of the Swedish 2004 edition of Clay Blair's "Hitler's U-boat War", then cross-referenced it with the commander files here at uboat.net, as well as some extra material (the interrogation reports available online, for example).

I was quite surprised to find that the casualty rates were so high even that early in the war. Out of the 49 captains who commanded subs on patrol during the time period in question, 33% were killed in action and an additional 12% were captured, during that very same time period (those who were killed or captured after August 31st 1940 are not included in that figure). So that's a total casualty rate of 45%.

I've seen mentioned somewhere that even the first of the "happy times" were not so happy after all, considerable gloom being brought by the casualties. These figures seem to confirm that.

If anyone is interested, I'd be happy to share my compiled data. I have it in OpenDocument format, but can also convert it to PDF or Excel format (although the formulas may become messed up in the latter format).

/ Tony