As icegreentea2 says, these are attack submarines, not part of the French strategic deterrent. In a surface attack role a nuclear sub has a significant speed a

As icegreentea2 says, these are attack submarines, not part of the French strategic deterrent. In a surface attack role a nuclear sub has a significant speed and endurance advantage. Conventional subs are can't adjust to course changes in targets very easily; of course, they are quieter and smaller, so choke point ambush becomes more feasible. A nuclear boat also has the speed to keep up with a carrier battle group or a fast convoy. The ability to use SLCM to strike land (MdCN) or maritime targets (Exocet) without obvious forewarning is also useful. Strategic boats are not used for conventional attack because it would reveal their location, and the launch of a ballistic missile could trigger real escalation towards nuclear exchange.