1 2 Martel, William C. (1998). “Why Ukraine gave up nuclear weapons: non-proliferation incentives and disincentives”. Trong Barry R. Schneider; William L. Dowdy (biên tập). Pulling Back from the Nuclear Brink: Reducing and Countering Nuclear Threats. Psychology Press. tr. 88–104. ISBN9780714648569. Truy cập ngày 6 tháng 8 năm 2014. There are some reports that Ukraine had established effective custody, but not operational control, of the cruise missiles and gravity bombs.... By early 1994 the only barrier to Ukraine's ability to exercise full operational control over the nuclear weapons on missiles and bombers deployed on its soil was its inability to circumvent Russian permissive action links (PALs).
