Mobile offshore base

In the defense industry of the United States, a mobile offshore base (MOB) sometimes called a Joint Mobile Offshore Base (JMOB) — is a concept for supporting military operations where conventional land bases are not available. Such a floating offshore base has been researched and proposed, but never developed.

A MOB is a modular floating base that can be deployed to provide flight, maintenance, supply and other forward logistics support operations. MOB modules will most likely be semi-submersibles which have significantly smaller wave-induced motions compared to conventional hulls.

This modularity supports the widest possible range of air support, ranging from vertical/short takeoff and landing (VSTOL) aircraft using a single module to conventional takeoff and landing (CTOL) aircraft using several serially aligned modules approaching 2 km (6,000 feet) in length. In addition, a MOB accepts ship-borne cargo, provides nominally 280,000 m² (3 million square feet) for equipment storage and maintenance, stores 40 million litres (10 million gallons) of fuel, houses up to 3,000 troops (an Army heavy brigade), and discharges resources to the shore via a variety of landing craft. The cluster could have an air strip that could hold a large aircraft such as the C-17.

History
The idea of the MOB was first seriously considered when the United States entered Operation Desert Shield (1990–91). The U.S. was forced to request the use of allied bases, which, besides strictly military considerations, proved to be politically sensitive in the case of Saudi Arabia. With the MOB concept the U.S. could have a base anywhere in the world in as little as a month. The base as conceived would have had virtually unlimited capabilities, and most of its creators did not envision just a floating air strip, but a town-sized base.

The "Joint Mobile Offshore Base" was a MOB concept for expeditionary warfare and humanitarian and commercial operations developed in the late 1990s by McDermott International, Inc. of Arlington, Virginia. The JMOB was to be composed of five self-powered units and a one-mile long runway that could accommodate a fully loaded C-17 Globemaster III. NATO was thought to be interested in the concept at the time.

A report presented to the U.S. Congress in April 2000 identified that such a base was technologically feasible and could be built by United States industry. A further report in 2001 by the Institute for Defense Analyses concluded that the estimated US$5 billion to US$8 billion was less cost effective than alternate solutions.

Once positioned, the MOB would operate as a base for an extended period, so it would need to have port-like facilities for unloading and loading conventional container and Roll-on/roll-off ships.

In fiction

 * In the video game Command & Conquer: Red Alert 3, the Empire faction has a mobile offshore base called Black Tortoise.
 * In Tom Clancy's Endwar one of the battlefields features the USS Reagan Seabase, a mobile operations and staging ship
 * In George Orwell's 1984, there are several mentions of mobile offshore bases called "Floating Fortresses"