You have to take into account that navy ships are quite complex and need intensive maintenance. A 60% availability at sea (which means a maximum of around 200 days at sea per year) is achieved only in the best navies, and that requires a huge investment in terms of maintenance support ashore.
Usually, a submarine or a navy ship will have a few weeks long missions followed by a one to three weeks stop use for maintenance, with a longer one every few cycles and a full stop for 10-18 months every 5 to 8 years.
So you really have around half your fleet available really.
Moreover, some of these submarines are used to protect the dissuasion sub forces. (special submarines that carry ballistic nuclear missiles so as to deter aggressors -USSR like really- from France's home territory).
In Europe, only britain and France have such a dissuasion force and would need to protect it.
A russian dissuasion sub firing a test missile
A french nuclear dissuasion task force submarine: A free fox in a free henhouse!
Well, it all gets into a completely different light if not all six are missile subs, but some are attack subs.
Damn the Swedish media and their fleeting relation to truth. Peak oil is not an energy crisis. It is a liquid fuel crisis.
France has six attack submarines, which it is planned to replace in the coming years (I don't really know when, because the government lacks money, as may have been said in the news) A free fox in a free henhouse!
