Lao candle As ” Disseminrz CHAPTER 1 INTRODUCTION 1.1 OBJECTIVE The immediate objective of tne crater survey, was to determine the dimensions of the apparent craters formed by Shots 1, 3, and 4. The long-range objectives of the work were to obtain data to assist in the prediction, for military purposes, of the crater produced by any large nuclear weapon fired under any circumstances. Two situations were of particular interest in this regard in Operation CASTLE. These were (a) a surface purst on land, and »b) a surface burst in relatively shal- low water. 1.2 MOLITARY SIGNIFICANCE The major military interest in craters stems from the observation that the limiting distance of important damage to well constructed underground fortifications lies only a relatively short distance outside the rater. For tne prediction of such damage it is clear that the shape of the crater near the rim is more important than its shape, or depth, near the center. Cf somewhat less military interest is the crater produced by a surface shot in shallow water. Botn the limiting distance of damage to tunnels and the possibility of damming a harbor by the formation of a crater with a shallow, or above-water lip, are matters of some concern. 1.3 LIMITATIONS ON THE OBJECTIVE: In the investigation of craters formed by smaller explosions it has been recognized that while the crater surface apparent to the eye was relatively easy to measure, there was nevertheless a disturbance in the earth, caused by the explosion, tc some depth below this upper surface. The lower boundary of this volume of disturbed earth has become known as the "true crater" in contradistinction to the upper surface, which has beer called the “apparent crater.' While the term "true crater" may be sligrttly misleading in its implications, it seems reasonably clear that for the purposes of determining the limitations of damage to underground fortifications the lower surface of the volume of disturbed earth