Update 1416 19 March: It looks like the attack has started. Based on open-source info, it looks like at least USS Providence (SSN 719), USS Scranton (SSN 756) and especially USS Florida (SSGN 728) might be in position to support the attacks. (A Pentagon briefing I'm listening to now confirms that submarines were part of the initial attack by U.S. and British naval forces, in which ~112 Tomahawks were fired at about 20 targets.)
It's amazing -- we're able to launch an attack even while President Obama is on a foreign trip. It's almost as if the President can do more than one thing at a time, and that he doesn't feel the need to micro-manage the On-Scene Commanders. I assume those who think he should have cancelled his trip believe the President should personally approve each missile fired by the military.
Update 1735 19 March: Here's confirmation from the Navy that those boats mentioned above were the three American submarines involved in the initial salvo of Operation Odyssey Dawn.