If Ukraine launches an offensive on any part of areas the Russians possess, they will be bombard from the air and sea. The Russians absolutely own both.
Yes, the Russians own the sea, especially the bottom of the Black Sea where the Moskva rests. Russian trolls even tried to attack Ukraine over missile strikes hitting civilian areas in Alchevsk, but I had the true story from friends in the town that the missiles hit an abandoned brewery that was used as a munitions depot. Secondary explosions continued through the middle of the night and closed the Alchevsk to Lugansk road.