Afloat Prepositioning Force

The Afloat Prepositioning Force is a fleet of cargo ships kept loaded with military equipment and parked near the world's likely trouble spots, so that troops can fly in light and marry up with tanks, ammunition, fuel, and field hospitals that are already there. The math behind it is blunt. Airlifting a heavy brigade takes weeks and hundreds of sorties. Sailing its equipment ahead of time and flying only the people cuts deployment from months to days.

The concept proved itself in 1990. When Iraq invaded Kuwait, prepositioning ships from Diego Garcia and Guam delivered equipment for the first Marine brigades in Saudi Arabia within two weeks, while units deploying from the continental US were still loading trains. Every serious American war plan since has leaned on the same trick.

How the force is organized

The ships belong to Military Sealift Command and sit in three groups. Marine Corps prepositioning squadrons, historically anchored at Diego Garcia in the Indian Ocean and Guam and Saipan in the Pacific, each carry roughly a Marine Expeditionary Brigade's worth of gear. Army prepositioned stocks afloat cover a heavy brigade plus port-opening equipment. A third slice carries Air Force munitions, Navy fleet hospitals, and Defense Logistics Agency fuel and supplies. Crews are civilian mariners, a detail that surprises people, and the ships cycle back to US ports every few years for maintenance of both hull and cargo.

The weakness is the same as the strength: everything is in the hull. A prepositioning ship needs a working port or a beach with lighterage to discharge, its location is no secret, and modern anti-ship missiles put a question mark over whether the ships could close a contested shore at all. That worry is currently reshaping the force toward more, smaller, more dispersed ships in the Pacific.

How is this different from a base?

A base needs a host government's permission, permanently. A ship needs none until the day it discharges, can reposition as a crisis builds, and can't be voted out by a foreign parliament. That political flexibility, more than cost, is why the US has kept equipment afloat since the late 1970s rather than relying purely on overseas depots.