Square Leg

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 British government. Part of the exercise involved a mock nuclear attack on Britain. It was assumed that 131 nuclear weapons would fall on Britain with a total yield of 205 megatons (69 ground burst; 62 air burst)[1] with yields of 500 KT to 3 MT [2] That was felt to be a reasonably realistic scenario, but the report stated that a total strike in excess of 1,000 megatons would be likely.

'Square Leg' target plot

Square leg is also a fielding position in cricket; see Fielding (cricket).

Mortality was estimated at 29 million (53 percent of the population); serious injuries at 7 million (12 percent); short-term survivors at 19 million (35 percent).

Square Leg was criticised for a number of reasons: the weapons used were exclusively in the high-yield megaton range, with an average of 1.5 megatons per bomb, but a realistic attack based on known Soviet capabilities would have seen mixed weapons yields, including many missile-based warheads in the low hundred kiloton range. Also, no targets in Inner London are attacked (for example, Whitehall, the centre of British government); towns such as Eastbourne are hit for no obvious reason.[3]

Operation Square Leg was one of the exercises used to estimate the destructiveness of a Soviet nuclear attack in the 1984 BBC production Threads.