Check out the Cormorant, a design concept from Lockheed Martin's famous Skunk Works:

The Cormorant, a stealthy, jet-powered, autonomous aircraft that could be outfitted with either short-range weapons or surveillance equipment, is designed to launch out of the Trident missile tubes in some of the U.S. Navy’s gigantic Cold War–era Ohio-class submarines. These formerly nuke-toting subs have become less useful in a military climate evolved to favor surgical strikes over nuclear stalemates, but the Cormorant could use their now-vacant tubes to provide another unmanned option for spying on or destroying targets near the coast.

The article goes into some more detail, including some of the engineering challenges facing such an unusual design.