The North Atlantic Treaty Organization (NATO) launched Operation ALLIED FORCE in response to Serbian President Slobodan Milosevic's campaign of ethnic cleansing of Kosovar Albanians. While the complex roots of ethnic tensions and violence in Southeastern Europe date many hundreds of years, Slobodan Milosevic initiated a new campaign of ethnic violence in 1989. This violence had taken the lives of more than 250,000 people by 1995, and spurred Kosovar Albanians desire for independence. When violence between Serb forces and Kosovar Albanians continued to escalate, the United Nations Security Council warned of an "impending humanitarian catastrophe" if action was not taken. Although a United Nations team travelled to Kosovo to observe the situation, they were helpless while Serbian forces attacked unarmed civilians. When peace negotiations were held in the spring of 1999, Milosevic massed forces along the Kosovo border. The Serbian President ultimately rejected all peace proposals and directed 40,000 troops into Kosovo, resulting in a massive refugee crisis.
Although NATO Secretary General Javier Solana did not authorize air strikes against Serbia until January 30, 1999, U.S. Air Force planners had worked out nearly 40 unique campaign options since the summer of 1998. The final air campaign plan was a "coercive operation," its primary purpose to force Milosevic's withdrawal from Kosovo. NATO leaders also rejected the use of ground troops, believing that air power could achieve the operation' s objective. The air campaign consisted of three phases: phase one focused on Serbian air defense systems; phase two called for strikes against military targets in Serbia below the 44th parallel and south to the Kosovo border; and in phase three airstrikes would seek targets north of the 44th parallel, including striking Serbia's capital Belgrade.
The first attacks occurred on the night of 24 March 1999, using 250 U.S. Aircraft, including 120 land based fighters, seven B-52s , six B-2s , ten reconnaissance aircraft, ten combat search and rescue aircraft, three airborne command and control platforms, and nearly 40 aerial refueling tankers. In addition, thirteen NATO member countries contributed aircraft. B-52s launched conventional air launched cruise missiles (CALCM) while U.S. and British ships and submarines fired Tomahawk land attack missiles (TLAMs). During the first night, the U.S. and NATO flew 400 missions, including 120 strike missions against 40 targets. On the second day of operations, U.S. Air Force F-15s shot down two Serbian MiG-29s, while another F-15C scored a kill the next day. Air Force and NATO aircraft faced significantly more effective air defenses than what they had recently encountered in Iraq, and pilots were initially instructed to stay above 15,000 feet to minimize risk.
When the phase one strikes did not achieve their intended effect on Milosevic, NATO proceeded with phase two strikes south of the 44th parallel. During this phase, the U.S. Air Force introduced B-1 bombers while NATO forces also averaged just 50 strikes per night. Realizing that it would take a more intensive effort to force Milosevic to withdraw his troops from Kosovo, NATO moved to phase three on the ninth day of the air offensive. U.S. Navy aircraft joined the operation on April 6, with the arrival of the aircraft carrier USS Theodore Roosevelt. Operation ALLIED FORCE had struggled to meet its objectives for several reasons, including poor weather, difficult terrain, and problems inherent in coordinating 18 allied air forces.
By the end of the third week, Supreme Allied Commander of NATO, General Wesley K. Clark, had a force of nearly 1,000 aircraft, 54 percent of which belonged to the U.S. Air Force. NATO's master target list reflected the pressure to escalate the air offensive as it grew from 169 to more than 970 targets by the time the campaign ended in June. The increased pressure also included strikes in Belgrade to demonstrate to Milosevic that the air campaign had reached a new level. For example, U.S. Air Force F-117 stealth fighters struck the electrical plant at Novi Sad, which cut off electricity to 70 percent of Serbia. Additionally, destruction of infrastructure targets resulted in more than 100,000 Serbians losing their jobs. Although there were flaws in target selection and verification, as well as civilian casualties during the air campaign, NATO tried to minimize the loss of life through strict rules of engagement, such as requiring positive visual identification before launching weapons.
During the 78-day campaign, sorties peaked in late May and early June. For example, on May 26, NATO aircraft flew nearly 900 sorties, and by June 2, 1999, Milosevic agreed to end the conflict. The terms of the agreement stipulated that Milosevic would withdraw his forces from Kosovo, a NATO-led force would provide security for the province; refugees would be allowed to return to their homes, and Kosovo would be granted self-rule under Yugoslav sovereignty. On June 10, the Serbian government ratified the agreement and Serbian forces began their withdrawal from Kosovo as elements of the Kosovo Force (KFOR) began to arrive. During ALLIED FORCE, NATO aircrews flew 38,004 sorties, 10,484 of which were strike sorties. During ALLIED FORCE, 29 percent of munitions dropped were precision guided, although 90 percent of aircraft were capable of employing them. The Air Force struck 421 fixed targets, 35 percent of which were destroyed. Overall, the U.S. Air Force flew 30,018 sorties, including 11,480 airlift, 8,889 fighter, 322 bomber, 6,959 tanker, 1,038 Intelligence, Surveillance, and Reconnaissance (ISR), 834 Special Operations, and 496 unmanned aerial vehicle (UAV) missions. Perhaps more importantly for the Air Force, the Air Expeditionary Force (AEF) concept was successfully used for the first time during ALLIED FORCE as units rotated into Aviano Air Base, Italy, under the AEF construct. Operation ALLIED FORCE also witnessed the first combat use of the B-2 Stealth bomber and the first significant employment of remotely piloted aircraft.