Apart from this being an amazing site for art-historians to explore, the u-boot scholar too will find it educational as it includes graphics pertaining to the main u-boot sites of St. Nazaire, Bordeaux and L'Orient:
http://bunkersite.com/bunkerart/
Note: When you enter go to 'search' at the bottom left and put in u-boot. Here you will be able to see some amazing pictures!
The rest of the site you can leisurely explore for yourself!