< PrevNext > 38. Northrop Grumman Falls Church, Va. Share 2018 U.S.-Booked Air Volume: $105 millionPrimary U.S. Online Booking Tool: ConcurPrimary U.S. Expense Supplier: ConcurConsolidated U.S. TMC: BCDDefense contractor and aerospace firm Northrop Grumman's U.S.-booked air travel increased slightly in 2018. Sales increased nearly 16 percent to $30.1 billion, and its backlog, a measure of firm orders not yet fulfilled, increased more than 25 percent to $53.5 billion. Northrop Grumman business travel—including air, rail, hotel and car rental—accounted for nearly 140,300 metric tons of carbon dioxide equivalent emissions in 2018, down about 2 percent year over year. The company had about 85,000 employees at the end of 2018, about 15,000 more than it did in 2017. Northrop Grumman added about 12,500 employees last year via the $9.2 billion acquisition of missile manufacturer Orbital ATK.