Fortress analogies can mislead naval strategy

Terry Pratchett's fictional Commander Vimes supplies a warning about defensive strongpoints: leave an enemy inside a magnificent fortress and take the territory outside it. The same reasoning exposes a limit of naval bastions, since a force that stays inside its defences yields freedom of action elsewhere. Land-warfare analogies become misleading when they turn a bastion into a boundary that ships cannot or will not cross. At sea, the barrier consists of patrols, surveillance and forces able to respond to contacts. NATO's GIUK defences and the Soviet bastion both depend on that active presence.