As L3 Technologies transforms itself from operating like a holding company to the defense industry’s sixth-largest company, it’s looking to invest in its core markets. Dallas-Fort Worth is arguably the defense contractor’s most important market. Two of the company’s three business units are headquartered in North Texas, and one in particular is looking to hire hundreds. “We have about 400 open requisitions in the Dallas region right now,” said Jeff Miller, the president of Intelligence, Surveillance & Reconnaissance Systems, or ISR. “I would say we’ll try and put half of those in the Plano office.” ISR moved into its new Plano headquarters about six months ago and is growing faster than expected. Of the more than 400 job openings, Miller said roughly half are for engineering positions.