The Pentagon has hired Boeing and Northrop Grumman to develop a replacement for the US Air Force’s arsenal of ageing Minuteman III intercontinental ballistic missiles (ICBMs) and cruise missiles, amid nuclear tensions with North Korea. "The Minuteman III is 45 years old. It is time to upgrade," Air Force Chief of Staff General David Goldfein said in a statement on Monday, three days after the deal for the new Ground-Based Strategic Deterrent (GBSD) was inked.