美国有些官员证实,美空军正在研究一种雷达事实上探测不到的无人攻击飞机,但他们又说,在设计和研制工作开展以前必须解决一些重要的技术上和操作上的问题. Some U.S. officials have confirmed that the U.S. air force is studying a virtually unmanned attack aircraft that the radar can not detect. However, they also said that some important technical and operational issues must be solved before the design and development work progresses.