Commando Comic #4873 'The Nightmare Fort' (2015)
 
Commander Ben Carter, RN, was on a secret mission for the Admiralty. He and his Motor Torpedo Boat crew were to rescue a secret agent - codenamed "Grey Falcon" - from the clutches of the Nazis on the French coast.

When they were ambushed, Ben started to wonder if he had a traitor in his midst.

Adrift in a lifeboat, Ben and the survivors unexpectedly chanced upon an imposing, Napoleonic sea fort and the mystery of what happened to their mission suddenly deepened...