The United States Army has established storage and maintenance facilities in East Europe. The Estonia, Latvia, Lithuania, Poland, Romania and Bulgaria facilities will support U.S. Army weapons and equipment that is already there or arriving by end of 2016. In the case of Hungary the equipment will not arrive until 2017. The U.S. already has the equipment for an armored brigade in the area and this is being moved further east, to Poland, Estonia and Latvia. These are among the few NATO members that are adjacent to Russia. In addition to the brigade worth of equipment (which includes 1,300 vehicles, a fifth of them armored) there will be smaller stockpiles of weapons and equipment for NATO allies in East Europe, for use if war breaks out.
The U.S. has similar stored equipment worldwide. Most of it is in warehouses or ships, while in Norway the prepositioned gear is kept in caves. This prepositioning of military equipment goes back to the 1960s when the U.S. began pulling combat divisions out of Europe but still wanted to be able to bring these units back quickly if the Russians threatened an invasion. The solution was prepositioned equipment for several divisions of soldiers and marines. After the Cold War ended in 1991 the army and marines adjusted their prepositioned equipment deployment. This involved moving some prepositioned gear to new potential hot spots. Throughout the Cold War, most of the prepositioned equipment was in Europe. Since the 1990s some was moved to the Persian Gulf and Korea. But one brigades worth was kept in Europe, and another was stored on ships off the Indian Ocean island of Diego Garcia. After the 2003 Iraq invasion there were three brigade sets in the Persian Gulf, one afloat off Guam, one in Korea and one still in Europe. The one in East Europe is currently used regularly for American brigades coming in to train and stand guard for nine months at a time.
This stored equipment has actually been used for something other than training exercises. Prepositioned gear got a workout during the 2002-7 Iraqi operations and the troops were very pleased with the reliability and readiness of the prepositioned gear. The equipment is maintained by civilians, under military supervision.
The prepositioned equipment for U.S. Marines is abroad ships. The U.S. Navy Maritime Prepositioning program cost about $7 million per ship per year to maintain. The navy MSC (Military Sealift Command) maintains sixteen of these ships, to carry heavy equipment and supplies. These ships are organized into three squadrons with one 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.
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 bomber aircraft 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, as do warehouses and ships in several countries and caves in Norway.