of so small a crater and it proved impossible to run cross wind in sufficiently straight courses to make taut wire measurements effective; hence, for two of the three runs a modified procedure was developed on the spot by which the boat's anchor cable was marked off, the boat was allowed to drift across the crater, and was then pulled back by the anchor winch. vr? ;9The post-Shot 3 aerial survey was made a few days after the shot but prior to Shot 4. From this survey a post-shot contour map showing, of ‘course, only the section above the waterline was constructed. << The post-Shot 3 fathometer survey was made on 1 May, the 24th day after the shot. Shot 4 had intervened and the water-wave resulting from Shot |oy had washed over the lip of the Shot 3 crater. This had the effect of! smoothing and lowering the lip to an unknown extent (believed to be slight); filling in the bottom of the crater and reducing the level of radioactivity. During the crater survey, the radiation level 10 ft above thewater surface was about 50 mr/hr and above the lip 1500 mr/hr to 3500 mr/hr, In the postshot survey in the vicinity of Shot 4 there was a Similar pressure of time. A barge was being put into place for a later shot and it was impossible to approach close to the presumed center of the Shot 4 crater. Three taut wire runs were obtained but for the reason just stated all are chords rather than diameters. Additional data in regard to this crater. were obtained from the Scripps Institution of Oceanography, who had ruma-fathometer survey two days previously to permit assurance to the captain?‘of the USS Curtiss that it was safe for the ship to proceed into the area,. The fathometer surveys in this area, as in the other craters, showed-‘a@ very flat bottom, obviously the result of filling-in of-md or fine sand to obscure the bottom of the crater. In addition to the fathometer data, information regarding lead-line depth and length of chain,og buoys and moors was obtained from the H&N group responsible for PHacempnt of the barge for the later shot. 23