The Damage Probability Computer for Point Targets with P & Q vulnerability numbers was created to provide military planners with a quick way of estimating the outcome of nuclear bomb attacks on overpressure-sensitive targets (PVNs) and dynamic pressure-sensitive targets (QVNs). PVN targets are destroyed by crushing [vertical blast pressure], QVN targets are destroyed by being knocked over [horizontal blast pressure]. A tank might be resistant to overpressure but capable of being tipped over by dynamic pressure effects. A hardened missile silo might be immune to dynamic pressure and have to be destroyed by overpressure.
The computer was first issued in 1974. A modified version, with an additional scale for calculating optimum air burst heights, was issued in 1977. The computer shown is the 1977 version. It is approximately 7 inches in diameter [18 cm] and is made of plastic. It was manufactured by Perrygraf.
At the time the US and the UK had a Single Integrated Operational Plan [SIOP] which listed all potential targets in the Warsaw Pact countries [and some other countries]. Each target was given a vulnerability number [see this post for an explanation of vulnerability numbers] and a desired probability of destruction. The desired probabilty was usually 0.75 but some targets were seen as more important and had higher probability numbers. What constituted ‘destruction’ was also defined for each target. For example, steel surface storage tanks had to be ruptured to be considered destroyed.
A point target is a small target which needs an accurate strike to destroy it. A city would not be a point target, a missile silo would.
Also, at this time the US and UK were introducing multiple independently targetable re-entry vehicles [MIRVs] to replace unitary warheads [a single, usually large, warhead]. The increase in the number of warheads allowed military planners to add a large number of targets to the SIOP. MIRVs carried more warheads but smaller ones.
The Poseidon Submarine Launched Ballistic Missile [SLBM], introduced in 1972, carried 10 or 14 W68 40 kiloton warheads [the Hiroshima bomb yielded 16 kilotons and the Nagasaki bomb 21 kilotons]. The Minuteman III had three 170 kiloton warheads. Such warheads could be used for point targets as well as city busting.
The computer only calculates blast effects. Thermal, cratering, ground shock and fallout [or other radiation] effects are not taken into account.
The red side of the computer is used for P targets (PVN) and the blue side for Q targets (QVN).
Inputs to the computer are – Continue reading