Navy leaders have defended the service's decision to wind up work on the X-47B unmanned combat air systems demonstrator (UCAS-D) in fiscal year 2015, turning aside encouragement from lawmakers to continue experimenting with the aircraft system -- built at a cost of nearly $1.5 billion. Supporters of continued UCAS-D experimentation argue the system has more than 80 percent of its service life remaining. On behalf of Navy Secretary Ray Mabus and then-Chief of Naval Operations Jonathan Greenert, the service earlier...
