"The Air Force reviewed Northrop Grumman’s preliminary design for the Ground Based Strategic Deterrent... advancing the program toward its next milestone and acquisition phase", the Air Force said in a statement.
The Air Force anticipates entering the next phase and awarding the engineering and development contract before the end of the fiscal year (30 September 2020).
Although the United States has reduced the number of nuclear warheads deployed on its long-range missiles and bombers, consistent with the terms of the 2010 New START Treaty, the US is also developing new delivery systems for deployment over the next 10-30 years, according to a recent report by the Congressional Research Service.
The New START is the last remaining arms control treaty in force between Russia and the United States after the collapse of the Intermediate-Range Nuclear Forces Treaty in 2019. The New START stipulates the reduction of the number of strategic nuclear missile launchers by one-half and limits the number of deployed strategic nuclear warheads to 1,550. The agreement is set to expire in February 2021, and the US has so far not announced plans to extend it.