21 November, NATO acted under its new authority with a strike on the Udbina airfield. The strike, which involved 39 aircraft, was the largest combat operation in NATO's history up to that time; nonetheless, it was criticized as a "pinprick" that did little real damage to Serb capabilities, only temporarily disabling runways. The NATO forces deliberately refrained from attacking Serb planes at the airfield, and only targeted runways and anti-aircraft capabilities. Following the Udbina strike, NATO continued to launch strikes in the area, and on 23 November, after a NATO reconnaissance plane was illuminated by the radar of a surface-to-air missile (SAM) system, NATO planes attacked SAM sites at Otoka and Dvor with AGM-88 HARM anti-radiation missiles. The Serbs reacted to these strikes by immediately seizing 250 UNPROFOR hostages, and a total of 500 by early December. While the hostages were treated fairly well, some were used as human shields, including three who were forced to lie on the tarmac at the Bosnian Serb airbase in Banja Luka. After the strikes at Otoka and Dvor, Bosnian Serb forces continued to target NATO aircraft with surface-to-air missiles, while advancing against the Bihać enclave. On 24 November, Serb forces fired radar-guided missiles at two British Tornado F3 aircraft. The next day, Serb forces fired on two NATO F-16s. In response to this growing SAM threat, and the UNPROFOR hostages, NATO suspended flights in Bosnian airspace on 2 December. Shortly after the suspension of NATO flights, former US President Jimmy Carter personally negotiated a four-month ceasefire in Bosnia. Although there were some violations of this ceasefire, most of the parties in the conflict heeded it. NATO ordered its planes back in the air, but due to the diminished hostilities, they did not engage in any significant operations for the next several months. The reduced tensions resulting from the Carter ceasefire and the cessation of NATO air operations also led to the release of most of the UNPROFOR hostages over the next several weeks. Expansion of the air campaign in 1995 Although 1994 ended peacefully with the Carter ceasefire, NATO continued planning for new operations. Both NATO and UN officials believed that after the ceasefire expired in March, the fighting would resume. As such, planners at the Balkans Combined Air Operations Center (CAOC) began drawing up plans for new air operations. By late December, the planners developed a plan called "Dead Eye", designed to