The U.S. Navy has contracted with Maersk Line (a Danish shipping company) to operate and maintain ten of its Maritime Prepositioning Force ships over the next five years. This will cost about $7 million a year per ship. The navy MSC (Military Sealift Command) maintains sixteen of these ships, to carry heavy equipment and supplies for the U.S. Marine Corps. These ships are organized into three squadrons, one each stationed in the Atlantic, Pacific and Indian Oceans. Each group of ships carries the equipment for a marine brigade and enough supplies it going for 30 days. All you have to do is fly the marines in, land the equipment, and you have a marine brigade ready to fight. The process takes less than a week.
In each squadron, equipment is dispersed among the five ships so that the loss of one ship does not eliminate an entire category of equipment. Thus each ship in the squadron carries approximately 15 M1A1 tanks, 28 AAVs (amphibious assault vehicles, armored carriers for infantry), 153 Humvees, 100 MTVR (heavy trucks that can carry 15 tons of stuff on a road, half that cross country), two mechanized landing craft, eight 155mm towed howitzers, and 550 containers filled with spare parts, ammunition, medical supplies, food, and other material needed to keep a Marine brigade (17,300 Marines and Sailors) going for 30 days. The MPF squadrons performed well during the 2003 Iraq campaign, with their stored equipment being ready for action when unloaded.
The army has weapons and equipment for seven brigades stored around the world, most of them on land. Three are in Europe, two in the Persian Gulf, one in Korea and one afloat in the Indian ocean. Most of the army's ships carry equipment for setting up ports and supplies for supporting troops and providing peacekeeping services. The air force, navy and Department of Defense each have three ships carrying fuel to support their operations in distant areas. The navy group includes a hospital ship.
With all these prepositioning ships, you can get a brigade of heavily armed troops, and another brigade of lightly armed paratroopers to an out of the way hot spot within a week. OK, what does that do for the cause of world peace or American interests? As it turns out, not a lot. Mainly because the hot spots most in need of marines or paratroopers are the same ones that have no impact on world affairs or American interests.
For decades the marines have had several battalions afloat at all times. These have been used mainly to help evacuate American embassies and local Americans when things get particularly ugly overseas. This has been the most frequent use of American troops overseas. The paratroopers have been flown off to emergencies less frequently.
The army's seven prepositioned brigades are largely in places left over from the Cold War (three brigades in Europe, one in Korea) The two in the Persian Gulf are a leftover of the 1991 Gulf War The one floating around the Indian the ocean could go to Africa or Indonesia, but there is little enthusiasm back home for such adventures.
A war, rather than peacekeeping or dealing with a small squabble, requires heavy (armored and mechanized) divisions. These have to be moved by ship and one major new development in sea movement since World War II is the high speed (twice as fast as regular transports) Ro-Ro (roll on roll off) ships. The U.S. has eight of these high speed Ro-Ro's, enough to carry an armored division.
The Roll on/Roll off angle is important, as it speeds up loading and unloading the ships considerably. It takes a day for military vehicles to drive ("roll") onto the ships, and less than a day to roll off. That's less than half the time required with a regular transport. The eight fast Ro-Ro ships carry as much as over a thousand C-5 or C-17 heavy air transports. The military would like to buy more fast Ro-Ro's. But over $10 billion was spent on new transport ships in the last 30 years. New fast Ro-Ro's cost over $100 million each.
Finding the money for something as unsexy as fast Ro-Ro's is difficult. If there's a major war, the current fleet will be adequate. Not just to move the troops, but also to carry the enormous amount of supplies (over a hundred pounds per soldier per day) to keep the troops in action. The 1991 Gulf War required the movement of seven million tons of stuff to supply half a million troops for six months.
Politics decides whether U.S. troops are used overseas, and politics can change. You can't quickly change your ability to move troops quickly. If you have to get a lot of firepower to a distant trouble spot, bombers don't always provide sufficient intimidation. Shiploads of tanks and troops deliver a more powerful message. In a world prone to random violence, ships that wait provide a quiet measure of security.