Operation Deny Flight was a North Atlantic Treaty Organization (NATO) operation that began on 12 April 1993 as the enforcement of a United Nations (UN) no-fly zone over Bosnia and Herzegovina. The United Nations and NATO later expanded the mission of the operation to include providing close air support for UN troops in Bosnia and carrying out coercive air strikes against targets in Bosnia. Twelve NATO members contributed forces to the operation and, by its end on 20 December 1995, NATO pilots had flown 100,420 sorties. The operation played an important role in shaping both the Bosnian War and NATO. The operation included the first combat engagement in NATO's history, a 28 February 1994 air battle over Banja Luka, and in April 1994, NATO aircraft first bombed ground targets in an operation near Goražde. These engagements helped show that NATO had adapted to the post-Cold War era and could operate in environments other than a major force-on-force engagement on the plains of Central Europe. Cooperation between the UN and NATO during the operation also helped pave the way for future joint operations. Although it helped establish UN–NATO relations, Deny Flight led to conflict between the two organizations. Most notably, significant tension arose between the two after UN peacekeepers were taken as hostages in response to NATO bombing. The operations of Deny Flight spanned more than two years of the Bosnian War and played an important role in the course of that conflict. The no-fly zone operations of Deny Flight proved successful in preventing significant use of air power by any side in the conflict. Additionally, the air strikes flown during Deny Flight led to Operation Deliberate Force, a massive NATO bombing campaign in Bosnia that played a key role in ending the war. Background and Operation Sky Monitor In October 1992, at the beginning of the Bosnian War, the United Nations Security Council passed Resolution 781. This resolution prohibited unauthorized military flights in Bosnian airspace. Following the resolution, NATO began Operation Sky Monitor during which NATO forces monitored violations of the no-fly zone, without taking any military action against violators. By April 1993, NATO forces had documented more than 500 violations of the no-fly zone. In response to these "blatant" violations of Bosnian air space, and implicitly of resolution 781, the UN Security Council issued Resolution 816. While Resolution 781 prohibited only military flights, Resolution 816 prohibited all flights in