The Air Force completed a key milestone last month in the development of a new reentry vehicle that will deliver the W87-1 warhead from the military's next-generation intercontinental ballistic missile system, the Ground Based Strategic Deterrent. The Mk21A program, intended to replace the legacy Minuteman III system's Mk21 reentry vehicle, successfully passed a system requirements review on Feb. 11, Air Force spokeswoman Leah Bryant told Inside Defense in an email Monday. The SRR marks an early achievement in the...