BAE Systems engineers are developing an experimental GPS-like undersea navigation system to enable manned submarines and unmanned underwater vehicles (UUVs) to navigate accurately with sonar beacons instead of inertial measurement units (IMUs) or global positioning system (GPS) satellite navigation. Officials of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., have chosen the BAE Systems sensor processing and exploitation group in Merrimack, N.H., for the Positioning System for Deep Ocean Navigation (POSYDON) program. The DARPA POSYDON program aims to develop an undersea navigation system to enhance the U.S. Navy's ability to provide precise positioning throughout the ocean basins while remaining below the ocean's surface, BAE officials say. The value of the contract was not released. POSYDON seeks to develop undersea navigation capability that enables submerged UUVs and submarines to navigate over long periods and long ranges without surfacing for a GPS fix to fine-tune their positioning.