Centre des systèmes d'information et de commandement de la Marine nationale

Very cool site!

Hard to find informations about this place... So secret that the navy command base is far from the see.

Force Oceanique Strategique [FOST] is headquartered at Houilles. This is the strategic command center for the French Naval Nuclear forces. Those 'mushrooms' may be canisters holding antennas that can be deployed ifthe others are destroyed. I would not be surprised if there was a lot of office space underground here.

FOST web site:
http://www.netmarine.net/forces/fost/

I found a reference from 2002 stating that "The SSBN command at Houilles (Yvelines) will be shut down and the command shifted to Brest."

Logical decision, Brest is a better place. I guess suppose that the mountain troops are headquartered at Tahiti.