The original sense of ground zero is the point on the earth’s surface at or directly below a nuclear detonation. The term dates to 1946. From the Chicago Daily Tribune of 30 June of that year:
Within a radius of one kilometer (.62 of a mile) from ground zero (the point beneath the blast center), men and animals died almost instantaneously from the tremendous blast pressue and heat; houses and other structures were smashed, crushed, and scattered; and fires broke out.
It was undoubtedly in military use prior to this, but no actual citations with unambiguous dates have been found. Ground zero appears in the U.S. Strategic Bombing Survey volumes on Hiroshima, but the date the survey was written is uncertain. The survey was conducted in October and November 1945, but the report was not issued until 1947:
Throughout this report the ground location of the point immediately under the burst is designated as ground zero, abbreviated to GZ, and the actual point of detonation in the air is designated as air zero, abbreviated to AZ.
Since that original sense, the term has been used for some other, related ones. During the Cold War, the outdoor cafe in the center of the Pentagon’s courtyard was jocularly labeled Ground Zero by wags in the Defense Department. Presumably the hamburger stand was the Soviet’s aim point. It is also used, to the despair of prescriptivists, as a synonym for square one, as in we’re back to ground zero. A fourth use is more on track with the original meaning, the center of any calamity or struggle, as in “South Africa is ground zero in the fight against AIDS.”
The specific use in the sense of the site of the World Trade Center on 11 September 2001 and afterwards falls somewhere between the sense of a nuclear bomb site and the center of a calamity. The name of whoever first used ground zero to refer to the WTC site is not known and it was probably independently applied to the WTC site by several people. All that is known is that by the end of the day on 11 September the phrase was on the lips of millions.
(Source: Proquest Historical Newspapers; ADS-L)
Copyright 1997-2017, by David Wilton