White Sub

Probably not a sub. Most likely a cover over the drydock.

Is not drydock, that is the pressure - Dock ;-)

The 1967 built pressure Dock of the Marinearsenals, a simulator for deep diving submarines, is considered unique in the world. Even Americans and Russians have nothing comparable.

In mausgrauen tube, especially in Germany built Militär-U-Boote thoroughly tested. Especially Bundeswehr and NATO partner, the services of the U-Boot-TÜV like to claim. How many of the floating fortresses here from all over the world were already at anchor, is also strictly secret, as construction data and simulated diving depths. The area is a military restricted zone.

http://www.stern.de/computer-technik/technik/:Marinetechnik-Mit-U-Boot-T%DCV/510423.html