Square Leg was a 1980 British government home defence Command Post and field exercise which tested the Transition to War and Home Defence roles of the Ministry of Defence and Government. Part of the exercise involved a mock nuclear attack on the British Isles. It was assumed that 131 nuclear weapons would fall on Britain with a total yield of 205 megatons (69 ground burst; 62 air burst) with yields of 500kt to 3mt This was felt to be a reasonably realistic scenario, although the report stated that a total strike in excess of 1,000 megatons would not be unexpected.