Russia is doing the exact same thing as we do in the Black Sea. They sail close to our territory as we do theirs. We do this in all seas and oceans as do they.
Surface ships can be seen and killed, theirs and ours. What you really need to worry about are submarines with ICBMs. They are hard to find, hard to see, and hard to kill. One Boomer Sub can destroy any nation on earth as a functional society. They are the ultimate weapon of war.