Designing and buying a new reentry vehicle for the Ground-Based Strategic Deterrent is expected to cost around $3 billion, although the Air Force isn't sure whether it will choose one or more contractors for the first development phase, a service spokeswoman said this week. Five major defense contractors -- Boeing, Lockheed Martin, Northrop Grumman, Orbital ATK and Raytheon -- are interested in competing as prime contractors for the Mark 21A reentry vehicle program's three-year technology-maturation and risk-reduction phase, the Air...