First designed in the 1960s at the height of the Cold War, the Minuteman nuclear weapons are starting to show their age, and replacement parts are difficult to find for the weapons designed in an analog age. Also aging are their silos, many built in the 1950s and now rusting as water seeps through the decaying concrete. Over the next 20 years, the US Air Force will switch out the entirety of its Minuteman III fleet with an as-yet-unnamed new missile known only as the Ground Based Strategic Deterrent (GBSD). The Air Force estimates the cost of the GBSD, to be introduced late in the 2020s and phased in over the following decade, will be around $86 billion over the missiles' life cycle of about 50 years.

Critics point to the Defense Department's long history of projects going way over budget and say the cost of replacing the nukes and maintaining their launch facilities is not warranted, given the tactical threats the United States currently faces. The Air Force "doesn't know how we are going to afford this," said Laicie Heeley, a nuclear expert at the Stimson Center, a nonpartisan anti-nuclear proliferation think tank in Washington. "Nuclear is crowding out more conventional systems that are (better suited to) the threats of today."

America's intercontinental ballistic missiles (ICBMs) are just one leg of its "triad" -- a three-pronged nuclear attack force also comprising submarines and bombers. The Pentagon wants to replace or modernize all three legs of the triad, at a cost experts estimate will hit $1 trillion over the next 30 years.

"We flat can't afford it. And from a priorities standpoint, it's the wrong priority in the world that we face," Democratic Congressman Adam Smith told a Washington forum last week, noting that the ICBM force is the part of the triad best suited for reduction.

The Pentagon insists it is imperative to push ahead with a complete overhaul of America's nuclear force. While the United States and Russia signed a treaty in 2010 to reduce the numbers of nuclear launchers, Moscow is modernizing its own triad. "The Russians, the Chinese, the North Koreans are upgrading all of their systems," an Air Force official told AFP, speaking on condition of anonymity to discuss the nuclear program. "They are upgrading all of their legs of the triad -- in that environment, I am not sure it makes sense" to do nothing.