viously used on Operations Tumbler and Jangle: Wianko balanced variable reluctance transducer type, connected to oscillograph recorders. All instrumen- noted that depth-of-penetration measurements were highly dependent upon the reliability of estimates of fallout below the ocean surface: the rate of descent of the fallout into the mixed layer must be slow enough to allow accessibility for measurement at the time of the survey. It appeared that for both Shots 5 and 6 this requirement was met, since (1) other fallout ob~ servations indicated a very-small particle size which could be expected to settle slowly and (2) from the depth-cast data of Shot 5, the descent of the radio— active material into the water masse comprising the mixed layer was of such a rate and uniformity as to tation functioned; good records were obtained, al- though the magnitude of the data was much less than predicted because of the low yield of Shot 3. The average values of the recorded free field data were: peak pressure at structure, 3.53 pai; dynamic pressure, 0.38 psi; and positive-phase duration, 1.52 seconds. Although the data obtained proved of considerable value as a check on the loading theory and the conclusions of related Upshot-Knothole Project 3.1, the immediate objective of the project was not met becauge the yield of Shot 3 was only 130 kt instead of the expected value of approximately 1 Mt. Neverthe- make depth-of-penetration calculations feasible. Project 2.7a “Radioactivity of Open-Sea Plankton Samples’ (WT-954), Scripps Institution of Oceanography, T. R. Folsom, Project Officer. less, the blast-loading data obtained was evaluated in This was not a formal Castle project, but represents work done incidental to Project 2.7 but of sufficient interest to warrant publication in the Castle the project reporta, and loading-prediction methods derived trom Upshot-Knothole Project 3.1—both the AFSWP-226 and ARF prediction procedures —can be WT series. considered to have been generally checked by this experiment. The objective of this study was to ascertain the general relationship pertinent to the uptake of fission products by marine organiams, in order to form a background for more-extensive tests that were to be conducted on Operation Wigwam. Samples of zoo¢-lankton were collected, and gross beta activities, neta-absorption curves, und gamma spectra were analyzed after identification of the orgumisms. A Project 3.2 “Crater Survey’? (WT-929), Stanford Research Institute (Assisted by Army Map Service); R. B. Vaile, Jr., Project Officer. The objective was to obtain dimensional data on craters formed by nuclear detonations for use in developing a generalized theoretical-empirical meangs of predicting crater dimensions. radiochemical analysis was performed by the U. 8S. Naval Radiological Defense Laboratory. In the preliminary planning for this project, con- It was found sideration was given to determining the dimensions of the true crater as well as those of the apparent crater. No feasible method of obtaining dependable data on the true crater—other than employing drilling or coring operations—~ was developed. The coat and operational problems involved outweighed the probable value of any data so obtained. Therefore, that (1) the feeding mechanism of the organism determined the amouit of activity assimilated, (2) solid phases in the water were concentrated in preference to the non-particulate phases, and (3) there was evi-~ dence of fractionation of isotopes by different groups of organisms. measurements were limited to those of the apparent PROGRAM 3: EFFECTS ON STRUCTURES crater. ‘The craters formed by Shots 1, 3, and 4 were measured. No measurements were made for other shots because they were detonated at the sites of Project 3.1 “Air Pressure Measurements” (WT-919), Stanford Research Institute; L. M. Swift, Project Officer. The objective was to obtain the air-blast loading pattern (as a function of time, in the 10-to-15-psi prior shot events. The measurement techniques emp’oyed were fa- overpressure region) imposed upon a rigid, r2ctan- gular parallelepiped by a megaton-range detonatic.. This data was desired as an extension of that obtained thometer traverses, lead-line soundings, and photo interpretation: A Navy NK-6 fathometer operating at 14.25 ke/sec by Upshot~Knothole Project 3.1 on target structures was mounted in an LCU which traversed the craters, of the same type and to develop techniques of predic- with horizontal control for these hydrograph surveys tion that could be applied to the calculations of struc- monitored by a combination of Raydist electronic- ture loading, response, and consequent damage from positioning equipment loaned by Navy Bureau of Aer- air blast from large-yield nuclear devices. The test structure was a 6-by~t-by-12-foot rigid onautics, Sextants, Alidades combined with gyrocompass, and anchored taut-wire equipment. concrete cubicle, with the 12-foot dimension normal to the path of the shock wave, located 9,500 feet from ground zero. A total of 46 gages were installed on the target structure; 12 pairs (24, total) were duplicates to ensure usable results. The gages were the type pre- Aerial-photography missions were flown to obtain pictures suitable for employment of stereoscopic photogrammetry techniques by the Army Map Service to provide detail ot any above-water crater phenom- ena. The body of knowledge regarding craters was ma- 111