The Sentinel (originally known as ASTOR, or Airborne STand-Off Radar) came about after the first Gulf War, which proved that effective aerial surveillence was an important part of winning modern battles. Raytheon's design to meet this standard was approved for production in December, 1999, with the aircraft first flying on May 26, 2004. The Sentinel R1 entered service in 2008, and a total of 5 have been built. These have been used in support of operations in Afghanistan and Libya, as well as in support of French troops in Mali. The UK's Strategic Defense and Security Review plans to retire the aircraft after their involvment in Afghanistan no longer requires it, and is planning to offer them to the NATO Alliance Ground Surveillence program.