Interestingly enough, the Navy is at present working on both of these ideas, after a fashion. The Ohio and the next boomer in the class (her name escapes me) are being removed from SLBM service and refitted as cruise missle carriers and SEAL transports. With the Tridents gone, they can carry something like 96 Tomahawks and still have room for a SEAL team and thier submersible.

Next submarine class is called the Virginia calss. It will be able to carry a seal sub on its back and be able to launch cruise missles.

Yeah, but the boomers can apparently carry one internally, and 96? the Virginia class won't even carry that many people, unless they are EXTREMELY friendly.