Northrop Grumman's plan to purchase Orbital ATK , announced earlier this month, marks the latest effort by some of the largest defense contractors to carve out new territory with acquisitions. In the last several years, contractors including Lockheed Martin and Raytheon have announced major acquisitions, picking up companies in areas they expect to grow. Northrop's deal to buy Orbital ATK, which it said would better position it in space and missiles, reflects a similar effort. The latest deals are a...