Ground Zero (GZ) and Air Zero (AZ) (1945 or 1947)

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THE UNITES STATES
STRATEGIC BOMBING SURVEY
_THE EFFECTS OF THE ATOMIC BOMB_
_ON HIROSHIMA, JAPAN_
   Volume 1 (Of three--ed.)
Physical Damage Division
Dates of Survey:
14 October--26 November 1945
Date of Publication:
May 1947

   It's a bit unfair to assign the "ground zero" found here to May 1947.
Surely, it was used in October 1945.
   The CATNYP entry shows "1945."  "SECRET" is right below the date.  This
was probably vetted long before it became available to the general public.

Pg. III (FOREWORD):  The United States Strategic Bombing Survey was
established by the Secretary of War on 3 November 1944, pursuant to a
directive from the late President Roosevelt.  Its mission was to conduct an
impartial and expert study of the effects of our aerial attack on Germany, to
be used in connection with air attacks on Japan and to establish a basis for
evaluating the importance nad potentialities of air power...

Pg. 91:
   SECTION VII
   DETERMINATION OF AIR ZERO

Pg. 92:
   _1. Summary_
   The point of burst o the atomic bomb is referred to as "zero," a point
determined to be in grid 5H approximately 700 feet southeast of the T-bridge,
at an elevation of slightly over 2,000 feet.   (...)
   _2.  Definition_
   The zero point may be defined as the point of detonation of the atomic
bomb.  The point had location in both plan and elevation, inasmuch as the
bomb burst in the air.  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.