The LGM-35 Sentinel, also known as the Ground Based Strategic Deterrent (GBSD), is a future American land-based intercontinental ballistic missile system (ICBM) currently in the early stages of development. It is slated to replace Minuteman III missiles, currently stationed in North Dakota, Wyoming, Montana, Nebraska, and Colorado, from 2029 through 2075. In 2020 the Department of the Air Force awarded defense contractor Northrop Grumman a $13.3 billion sole-source contract for development of the LGM-35 after Boeing withdrew its proposal. Northrop Grumman's subcontractors on the LGM-35 include Lockheed Martin, General Dynamics, Bechtel, Honeywell, Aerojet Rocketdyne, Parsons, Textron, and others. History In 2010, the ICBM Coalition, legislators from states that house nuclear missiles, told President Obama they would not support ratification of the New START treaty with Russia unless Obama agreed to revamp the US nuclear triad: nuclear missiles that could be launched from land, sea, and air. In a written statement, President Obama agreed to "modernize or replace" all three legs of the triad. A request for proposal for development and maintenance of a next-generation nuclear ICBM was made by the US Air Force Nuclear Weapons Center in July 2016. The GBSD would replace the Minuteman III, which was first deployed in 1970, in the land-based portion of the US nuclear triad. The new missiles, to be phased in over a decade from the late 2020s, are estimated over a fifty-year life cycle to cost around $264 billion. Boeing and Northrop Grumman competed for the contract. In August 2017, the Air Force awarded three-year development contracts to Boeing and Northrop Grumman for $349 million and $329 million, respectively. One of these companies was to be selected to produce a ground-based nuclear ICBM in 2020. In 2029, the GBSD program is expected to enter service and remain active until 2075. On 25 July 2019, Boeing announced it would not place a bid for the program, citing Northrop's recent acquisition of Orbital ATK (now Northrop Grumman Innovation Systems), Boeing's supplier of solid rocket motors. Northrop signed an agreement to firewall Boeing's proprietary data after acquiring Orbital ATK. The Air Force has since halted funding for the Boeing project, leaving Northrop Grumman as the sole bidder. In December 2019, it was announced that Northrop Grumman won the competition to build the future ICBM. Northrop won by default, as their bid was the only one left to be considered for the GBSD program. The Air