The first two production model Global Hawk (RQ-4B) UAVs have entered service. While the Global Hawk has been in use since September 11, 2001, it was doing so as an aircraft still in development. Global Hawks flew 8,000 hours of combat missions in the last four years, while development was completed and before regular production could begin. Several years of development were cut, because of the large number of combat missions the development aircraft were flying. The RQ-4A development models were just starting flight testing in 2001. The tests were going so well that, when 911 came along, it was decided to start using the RQ-4A for combat missions. That worked, up to a point. RQ-4As were lost after about a thousand flight hours for the first few years, because of problems that usually show up during development (or, as they say in the computer business, in "beta test"). That adds up to pretty expensive flight time for an aircraft costing, initially, $30 million each (current price is $70 million). Currently, about 49 RQ-4Bs are on order.