As cost estimates for the Lockheed Martin F-35 continue rising, some US lawmakers are pushing military officials to increase spending on fourth-generation fighters as a back-up. Senator Joseph Lieberman of Connecticut says he considers the F-35 a "really extraordinary aircraft", but is concerned about the military's projected tactical aircraft shortfalls. "There will certainly be pressure to sustain the fourth generation and improvement of aircraft because the fifth generation is coming on more slowly and more expensively than we hoped for," Lieberman told a Senate hearing on the tactical aircraft budget on 13 April. The US Navy has projected a 243-aircraft...