In order to meet disarmament treaty obligations, the United States is retiring it's most recent ICBM design, the Peacekeeper (formerly called the MX). Older Minuteman III ICBMs will be upgraded to replace the retired missiles. The Peacekeeper entered service in 1986, as the ultimate Cold War era ICBM. Only 23 Peacekeepers are still in service, out of  50 originally deployed. 

The upgrading of the older Minuteman III missiles has been under way for several years. The air force is in the process of replacing the decades old solid fuel rockets of its 500 Minuteman III missiles. Actually, a test of a 33 year old Minuteman I rocket motor showed that the motor (actually, a long tube full of slow burning explosives) still performed according to specification. The last of the Minuteman III missiles will receive their new motors by 2008. It costs about $5.2 million to replace the rockets on each missile. The new rocket motors, which have to comply with EPA (Environmental Protection Agency) rules, will have a shorter range (which was classified, but thought to be nearly 10,000 kilometers, based on where the missiles were stationed and where likely Russian targets were.) than the original motors 

The Minuteman III guidance systems and control electronics, in the silo and launch center, are also being upgraded. The Minuteman III entered service in 1968, while the Minuteman I became operational in 1962, as the first solid fueled ICBM. 

Finally, to comply with disarmament agreements, the Minuteman third stage, that contains three 440 pound nuclear weapons, will be replaced with a warhead containing one 600 pound nuclear weapon. 

The Minuteman III is 70 feet long, 5.5 feet in diameter and weighs 32 tons. The Peacekeeper is a four stage missile that carries ten warheads. The Peacekeeper is  71 feet long, 7.7 feet in diameter and weighs 88 tons. 

The Peacekeeper has the same range as the Minuteman III, but greater accuracy. The refurbished Minuteman IIIs will have the same accuracy as the Peacekeeper. Because the Peacekeeper came into use just as the Cold War unexpectedly ended, only fifty were ever put into service. The upgraded Minuteman III is expected to remain in service until 2020, at which point it will be replaced by a new missile design. Current disarmament treaties have the United States reducing nuclear warheads getting below 2,200 in the next few years.