Given the availability of nuclear weapons with surface detonating laydown delivery, however, there was little or no development of conventional deep penetrating bombs until the 1991 Gulf War. During the Gulf War, the need for a conventional deep penetrator became clear. In three weeks, a cooperative effort directed by the Armament Systems Division at Eglin Air Force Base in Florida developed the 5,000-pound (2,300 kg) GBU-28 that was used successfully by F-111Fs against a deep underground complex not far from Baghdad just before the end of the war.[citation needed]