thumb|right|'Square Leg' target plot
Square Leg was a British government home defence Command Post and field exercise which was held from 11 to 25 September 1980 and which tested the Transition to War and Home Defence roles of the Ministry of Defence and British government. Part of the exercise involved a mock nuclear attack on Britain; the exercise scenario of 150 nuclear weapons striking Britain, with the majority of these weapons having a yield ranging from 500 kilotons to 3 megatons and a resulting total yield of 280.5 megatons, was felt to be reasonably realistic, but the post-exercise report stated that a total strike in excess of 1,000 megatons would be more likely. with underwater bursts also being depicted. While official casualty figures were not provided, Stan Openshaw and Philip Steadman produced an independent estimate of 29 million deaths (53 percent of the population) and 7 million seriously injured (12 percent), with short-term survivors numbering 19 million (35 percent). towns such as Eastbourne were hit for no obvious reason.