russia, syria and lebanon have been saying they will strike back at wherever an attack comes from. obviously the latter two aren't cause for worry but russia's fleet based in syria is currently conducting a missile launching exercise at sea, in good position to retaliate.
also noteworthy, additional refueling planes and f-16s have been sent to the US' incirlik base in the last 24 hours. whether its a scheduled rotation is unclear, though.
The Russians deployed several S-400s in Damascus a few years ago, those can intercept most planes and remotely launched large missiles. I don't know about the whole "Lebanon retaliating" thing tho, considering that last bombing was from Israelis jets in Lebanese airspace attacking that air field.
yeah, like i said, its not like lebanon or syria are much of a threat but they have said they'd retaliate. cnn has a piece speculating what might be used and their best guesses were air launched american jassm missiles or european storm shadow missiles since they are newer and more difficult to intercept than tomahawks and can still be fired at pretty much any target in syria from outside it's borders.
Why subs and not destroyers? A couple small missile boats would be cheaper and more effective than deploying submarines against a non-existent naval threat