Boeing Co beat out Lockheed Martin to retain its position as the prime contractor for the US long-range missile shield, the Pentagon said on Friday.The US Defense Department said it was awarding Boeing a $3.48 billion, seven-year contract to develop, test, engineer and manufacture missile defense systems.A team led by Lockheed Martin Corp and Raytheon Co had vied with Boeing to expand and maintain the Ground-based Midcourse Defense, or GMD, hub of layered antimissile protection.Boeing partnered with Northrop Grumman Corp to retain the work.