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The Sea Base: A Status Report

The Sea Base has moved quietly from an expression of an aspect of seapower to a central means of supporting Marine Corps strategy. The Marines gain enormously from the extent to which they can use the sea, rather than part of the land, as a maneuver space. Although vehicles can move quickly over the land, only the sea offers the ability to move really massive tonnages quickly. Using maneuver, a more mobile force can attack an enemy’s weak points, such as his flanks. An enemy trying to cover the entire area vulnerable to the maneuvering force inevitably weakens himself at all points. For example, during the 1991 Gulf War, the Iraqis had to face not only ground forces approaching from Saudi Arabia, but also a Marine force that could cross the beach anywhere in Kuwait. The Iraqis felt compelled to dig several divisions into the beach, fatally weakening their force on the Saudi border.

For the Marine Corps, the evolution of amphibious assault has been a study of sea-based maneuver. During the Cold War, the U.S. Navy’s Maritime Strategy stressed the ability of the sea-based force to land on the flanks of an advancing Soviet army, compelling it to stop to defend itself, and thus contributing heavily to the defense of Western Europe. To make that threat credible, the Marines had to be able to cross a greater and greater variety of beaches; otherwise an enemy could guess where they would attack. The air-cushion landing vehicle (LCAC) was designed to provide exactly this extended capability. The flexibility of the assaulting force made it

A U.S. Navy graphic depicts some of the existing and notional vessels comprising the Sea Base. U.S. Navy imagery.

almost impossible for a defender to choose beaches to fortify (the short Kuwaiti coastline was an exception), so Marine tactics envisaged a quick build up on the beach before a mobile enemy defending force could get into place.

The build-up was needed because there was no way to go directly from ships to the objective beyond the beach. Since before World War II, ships have been combat-loaded. What comes off first is what will be needed in the initial fight to secure the beach. Everything else is packed in behind this urgent cargo, on the understanding that it will be spread out on the beach (what is sometimes called the “iron mountain”) to form a base for the force going inland. The logistical bottleneck on the beach becomes a lucrative enemy target. Moreover, once the base on the beach has been built up, it limits the flexibility of the Marine force moving toward its inland target. An enemy watching the build-up is no longer entirely subject to the sort of surprise that maneuver warfare is supposed to provide.

The question early in this decade was whether the logistical mountain could be kept offshore, where it could keep moving even after combat Marines were ashore and moving inland. That is the concept of the Sea Base. Not only would the Sea Base make the Marines more maneuverable, but not building up on the beach would also make it easier to withdraw the Marines once they had completed their mission so that they could quickly be redeployed. That kind of strategic flexibility becomes more and more important in a world of quick crises widely spread, where U.S. forces are very limited in manpower.

Several things have to be done to make it work. First, the ships have to be rearranged so that whatever is needed by the troops is instantly available. Combat loading was adopted because ship space was relatively scarce. Holds were deep, and access typically was only from above, by shipboard crane (container ships do not solve this problem). What is needed is a ship arranged internally more like a huge store than like a warehouse, with anything equally accessible. It happens that the Navy has been building major logistics ships in just this way for some years. Compared to earlier ships, they are much larger for the payloads they carry, simply because they need all that open space for access (like the aisles of supermarkets). For a given number of ships of a given size, whatever is offshore will be less than in the past, but a lot more accessible.

The United States already operates a Maritime Prepositioning Force (MPF) of large merchant ships loaded with equipment, to match up with troops flown in. An MPF squadron of four ships carries the heavy equipment of a Marine Expeditionary Brigade (MEB). Originally, the MPF was seen as a way of building forces very quickly to match Soviet attacks, particularly in the Gulf area. It proved its value during the build-up after Saddam Hussein invaded Kuwait. The MPF, however, cannot form a Sea Base, not least because it is designed to unload the equipment at a friendly port with a nearby airfield. However, when MPF ships had to be replaced early in this decade, it occurred to Marine and Navy strategists that the next-generation ships might be designed so that they could also form a Sea Base.

Sea basing is a further evolution of a Navy/Marine expeditionary strategy developed after the 9/11 attacks highlighted the need for flexible forces capable of handling widespread crises. The basic Marine force is six MEBs, three on each coast. Soon after 9/11 the Navy developed the concept of an Expeditionary Strike Group (ESG) built around the Marine Expeditionary Unit (MEU) and sufficient amphibious and support ships. One major flaw in the ESG concept is that the MEU is not envisaged as a fully self-supporting unit; the Marine Corps is MEB-, not MEU-, centric. A MEB comprises three MEUs plus considerably more in the way of supporting arms and supporting supplies. That is why each of three prepositioning squadrons was conceived to match an MEB.

The Military Sealift Command roll-on, roll-off container ship USNS 2nd LT John Bobo (T-AK 3008) is moored to the causeway of the Improved Navy Lighterage System (INLS) as the INLS causeway ferries, right, and roll-on, roll-off discharge facility, center, stand by to transfer Marine vehicles to the high speed vessel Swift (HSV 2), left, as part of the Navy’s West Africa Training Cruise 08 (WATC), a sea basing initiative in conjunction with Africa Partnership Station. U.S. Navy photo by Mass Communication Specialist 2nd Class Elizabeth Merriam.

Similarly, the Sea Base is conceived as the rear echelon of an MEB. A typical operation would begin with projection ashore, under cover of darkness, of one surface and one vertically delivered element of a MEU (three of which are incorporated in the MEB). The Sea Base would house the rest of the MEB, including its third MEU (which could be projected either on the surface or by air).

In March 2006, the projected future Sea Base was defined as 14 ships, 12 new and 2 existing dense-pack ships (which could not therefore effectively serve the Sea Base): two LHA 6 amphibious carriers (Marine Expeditionary Brigade command and control), one LHD (aviation command/control), three modified large-medium speed roll-on/roll-off (LMSR), three Lewis and Clark-class T-AKE, and three MLPs (the floating piers described below). Note that it takes about three times as many ships to support a MEB on a Sea Base (continuous supply) basis as via the earlier prepositioning force. That is because all items in the Sea Base must always be accessible.

Plans for new-design ships, including ones with flight decks (for V-22s) and with LCAC loading facilities were approved for the future Maritime Prepositioning Force about 2003, but were later dropped as unaffordable. Later, the first MLP was included in the FY 09 program. It was the only new-design ship in the package. All of the elements of the Sea Base are now approaching production. The ships will be the Navy’s now-standard logistics ship, the Lewis and Clark-class T-AKE. These ships are already designed for quick access to anything they carry, which is why they are so large. However, they are not designed specifically to handle large items such as tanks. Had they not been included in the Sea Base, the LHD and two LHA would have formed the core of three ESGs, so the new concept is to reduce to nine ESG plus the Sea Base force. In 2006, the Navy claimed that the new force structure would support simultaneous forced entry by 3.5 MEBs, with two more following from a sustained Sea Base. The Sea Base carries 20 days of supplies for its MEB.

The Sea Base cannot operate in isolation. Its creators assumed that it would be supported by an intermediate base within 2,500 miles. There has to be some way to bring further supplies to the Sea Base. Moving heavy cargo from ship to ship is likely to be inefficient; the floating pier envisaged as part of the Sea Base is not a floating container port. However, it is possible to envisage a steady exchange of Sea Base ships between the intermediate base and the Sea Base. The intermediate base might also be where Marines themselves arrive by air, for the relatively short transfer by sea to the Sea Base and thence to the fighting force inland. A 2004 description of the concept of operation showed an advance land base to support a Sea Base 2,000 nautical miles further forward, itself more than 100 nautical miles from the beach. The expeditionary force supported by the Sea Base might push to an objective within about 200 nautical miles of the beach. Forces had to be inserted, over a range of 100 nautical miles, in 8 hours (i.e., in darkness, to minimize vulnerability), in Sea State 4. At present the LCAC limits the range of surface insertion to 50 nautical miles, hence the need for something new. Air insertion range is limited to 135 to 150 nautical miles, and airlift sustainment is similarly limited.

A landing craft air cushion, or LCAC, flies onto the flat deck of heavy lift ship MV Mighty Servant I to load equipment and supplies for transport to shore during a Mobile Landing Platform demonstration near San Diego. Rob Wolf photo.

Given the ships, whatever is on board has to be brought to those fighting inland. The current approach is to develop a ”connector,” a fast beaching craft that can run from the base well offshore to the beach. Vehicles on board a connector would make the rest of the trip inland. The V-22 Osprey and similar aircraft could also function as connectors, providing more urgent supplies to the moving Marine force. The faster the connector, the further offshore the Sea Base can be, and the more it can maneuver (not least to avoid enemy targeting). The connector was initially called the High Speed Connector (HSC).

In June 2004, the Commanding General, Marine Corps Combat Development Command signed an Enabling Concept for the High Speed Connector (HSC). It (and the LCAC replacement) has also been called the Ship to Shore Connector (SSC). After some studies, in August 2005, the Office of Naval Research solicited proposals for a prototype Transformable Craft (T-Craft), which could deploy unloaded 2,500 nautical miles from the intermediate support base to the Sea Base, and then function as connector, transporting vehicles to the beach. The craft was called transformable because it was assumed that sustained high-speed runs in the open sea would demand something different from the run from the base to the beach. At the time, the Army and Navy were much impressed by specialized high-speed open-ocean craft such as the catamaran HSV, which are utterly unable to beach, or even to survive in very shallow water. The difficult open-ocean requirement was levied on the theory that such a craft would be too large to be accommodated on board the specialized amphibious ships with internal docks. However, if the MLP (see below) is a Float-On/Float-Off (FLO-FLO) ship, it can transport much larger craft over long distances, and it can launch and retrieve them without needing a dock. In that case connector design may be greatly simplified.

The connector had to run at high speed in shallow water (envisaged as 6 to 14 feet deep), and also to traverse offshore sand bars and mud flats to land well inshore. Because this is not too different from what the LCAC can already do, the connector has often been described as a replacement LCAC. However, the long-range deployment requirement is beyond LCAC capability. ONR envisaged a Sea Base 100 to 200 miles offshore. Initially, ONR was interested in several alternative sizes, the smallest being about 170 feet by 50 feet, capable of transporting over 200 tons at 40 knots or more. It envisaged a crew of two (maximum of three). For the unloaded deployment mode, ONR wanted a range of 2,500 nautical miles at 20 knots in Sea State 5. However, the craft had to operate in the open ocean in Sea State 6, and survive in Sea State 8. The transit to the beach at 40 knots or more might be in Sea State 4. Maximum unrefueled range in high-speed/shallow-water mode would be 500 to 600 nautical miles at 40 knots. In order to load in Sea State 4/5, the craft should be able to mitigate wave-induced motion (which an LCAC cannot do). The objective was a capacity for 750 long tons of cargo (minimum acceptable was 300) with a payload area of 5,500 square feet (minimum acceptable was 2,200). The Office of Naval Research (ONR) expected to award multiple preliminary design contracts as Phase I, two detailed design contracts as Phase II, and a single prototype as Phase III.

Textron imagery of its proposed T-Craft, capable of operating as a catamaran, surface effect ship, and air cushion vehicle. Imagery courtesy of Textron Marine and Land Systems.

As described in 2009, ONR envisaged a craft that would combine catamaran operation at sea, an air cushion for the ride to the beach, and perhaps a surface effect hull.

However, in 2006 the Navy described the SSC in much more conservative terms, with double the 72-ton load carried by an LCAC.

ONR awarded Phase II contracts to Alion Science and Technology (Raytheon, Nichols Brothers, and CDI Marine), to Textron Marine (which makes the LCAC: the team included CDI Marine, the Naval Surface Warfare Center at Panama City, L-3, Jacobs Engineering, the Littoral Research Group, and MiNO Marine), and to Umoe Mandal (Goodrich EPP, Island Engineering, FIReCo AS, General Atomics, Ultra Poly, Griffon Hovercraft, Applica, MIT, and Halter Marine). ONR published a typical scenario, in which the craft was launched about 270 nautical miles east of Norfolk, Va. It spent most of its time as a Surface Effect Ship (SES). About 1,000 miles off the beach it transitioned into amphibious mode. Total mission time was 6.75 hours, carrying 500 long tons of cargo. ONR pointed out that such a ship could reach anywhere on the mid-Atlantic seaboard (Cape Cod, Ma., to Cape Hatteras, N.C.) if it could sustain 40 knots for 6 hours.

Alion is offering a Surface Effect Ship that transforms into a fully cushioned vehicle to become amphibious. It is about 280 feet by 80 feet, displacing about 2,000 tons fully loaded, capable of carrying six Abrams tanks. Umoe Mandal also offers a hybrid SES and air cushion craft, based on the Norwegian Skjold-class fast-attack boat (an LCS candidate based on that design was rejected). Textron is offering a hybrid catamaran air cushion design, which can operate as a catamaran at low speed and in a low sea state, as an SES at high speed or in high sea state, and as an air cushion vehicle to go in over the beach. A Textron publicity release distinguished the projected LCAC successor (to be fielded in 2019) from the T-Craft.

The Navy completed an at sea exercise in February 2010 to demonstrate the transfer of vehicles between a surrogate Mobile Landing Platform (MLP) ship and a large medium-speed roll-on/roll-off (LMSR) ship. The test, led by the Strategic Theater Sealift Office within the Navy’s Program Executive Office Ships (PEO Ships), was part of risk-reduction efforts for the Department of Defense Maritime Prepositioning Force (Future) when transferring military vehicles between ships at sea. The test demonstrated a self-deploying ramp system installed on the surrogate MLP, semi-submersible MV Mighty Servant 3, and a new self-deploying sideport platform installed on the Military Sealift Command large, medium-speed roll-on/roll-off ship USNS Soderman. The goal of the testing and the program is to provide the capability to the U.S. military for large-scale logistics movements from sea to shore without dependency on foreign ports. U.S. Navy photo.

A third element is the Mobile Logistics (or Landing) Platform (MLP), the “pier in the sea” onto which the offshore ships unload, and from which the connector can take its cargo. The pier is needed because the ships cannot easily unload directly onto the connector. Experience since the beginning of World War II has shown that it is nearly impossible to unload vehicles and other heavy cargo by crane into a small beaching craft bouncing about alongside a cargo ship. That is why the U.S. Navy has incorporated docks (for loading) into so many amphibious ships. The docks in turn limit the size of beaching craft such as the LCAC, and it is unlikely that they will grow much to accommodate substantially larger craft, such as the future Connector. A pier is a different proposition. The great question is whether a viable floating pier can be built, given that both it and the unloading ship will be moving in the water. The existing well-developed technology of under way replenishment is not much help, because the items involved are so much smaller than what has to be transferred in and out of the offshore base.

The best hope for fast cargo transfer from the Sea Base ships is to load cargo directly from the roll-on/roll-off ships onto the MLP, which could transfer it to the Connector. As initially described, the MLP would be an 800-foot heavy-lift float-on/float-off (FLO-FLO) ship capable of carrying about 1,100 (later 800) Marines plus LCACs. As a semi-submersible FLO-FLO, the ship could carry its own cargo and Marines large distances through high seas, then flood down so that cargo could be transferred onto its flat deck. Presumably a flooded-down FLO-FLO enjoys minimal movement with the sea (how it coordinates with a moving conventional ship may be another story). The ability to carry Marines was later deleted, the designers concentrating on the essential cargo transfer role. It was hoped that the MLP could take on cargo while under way, then load LCACs hovering above its flat deck. Early MLP concepts had the ship carrying up to six LCACs (presumably fewer Connectors). The initial test (2006) used the chartered heavy-lift ship Mighty Servant as the surrogate MLP and the LMSR Watkins. The two anchored side by side in calm waters in Puget Sound, Wash., and moved cargo via the side ramp on the LMSR. Off San Diego, Calif., the Mighty Servant was then able to load cargo onto LCACs. These calm-water successes were no great surprise; the real test of the MLP is in rough water. The rougher the water it can handle, the further offshore the Sea Base can be (and the greater the percentage of time it can function). It would not do the Marines ashore much good if a heavy swell cut them off from their floating beachhead.

In October 2006, off Norfolk, the surrogate MLP Mighty Servant 3 moored alongside the LMSR Red Cloud while both were under way. Red Cloud offloaded vehicles onto the FLO-FLO using her own side ramp, which is more normally used at a pier.  Mighty Servant 3 is a 594-foot FLO-FLO (semisubmersible) heavy-lift ship with a large flat deck. LCACs easily flew onto the flat deck of the FLO-FLO to take the cargo aboard via their own ramps, then left for the beach. In a February 2010 test, the surrogate MLP Mighty Servant 3 was provided with a self-deploying ramp. The LMSR Soderman had a new self-deploying sideport platform. Making the transfer less direct probably made it easier to overcome sea motion. In Sea State 3 and low Sea State 4 in the Gulf of Mexico personnel and vehicles, including main battle tanks, were successfully transferred over several days. As of early 2010, the design contract for the MLP had been let to NASSCO, which already builds the Lewis and Clark class. The first ship is to be laid down in 2011.

This article was first published in Marine Corps Outlook: 2010-2011 Edition.


Norman Friedman is an internationally known strategist and naval historian. He is the author of...