Shipborne Marines make deterrent deployments reversible

A beach cannot be closed by cyber attack in the same way as a port, while mining it would visibly cross a threshold toward war. Amphibious forces can therefore serve as tools of grey-zone deterrence and conflict management as well as assault formations. A shipborne Royal Marines force can arrive, exercise with an ally, signal resolve, and remain offshore while political circumstances develop. If intervention is no longer desirable, the force can depart without extracting troops already based inside allied territory. Airborne forces remain available for crises that emerge too quickly to anticipate.