Looking through the Mulligan article again, it has some interesting stats on the age distribution, geographic origin, and civilian occupation of the U-Boat crews he was able to piece together.
Here's the table showing the civilian occupation of the U-boat crews he studied (edit: I don't remember his methodology and I'm too lazy to read the article again right now)--clearly he was only able to gather this particular info on a limited number of crew members (edit:again, I don't remember if this was a random sample or just a limited sampe size, again, I'm too lazy to re-read the article right now), however, it's still an interesting table.
Pretty interesting stuff really. If you want the .pdf, let me know.
J