ADELANTO - General Atomics Aeronautical Systems will begin work on its latest unmanned aircraft system under the first $6 million installment of a development contract for the Army. The Warrior is based on the company's Predator unmanned vehicle, a system already proven successful in combat over Afghanistan and Iraq. The entire program, including eventual follow-on production, is worth just under $1 billion, said Kimberly Kasitz , General Atomics spokeswoman. "It's a major contract for us," she said. The new system is expected to replace the Army's existing unmanned reconnaissance system, the Northrop Grumman Co.-built Hunter, which entered service in 1996....