<a _ long duration positive-phase air blast. Six steel-frame industrial buildings were tested in Operation Redwing: three drag-type structures, 30 ft in height, 40 ft in span, and 40 ft in length; and three semidrag-type structures, 30 ft in height, 40 ft in span, and 80 ft in length. These buildings were located on Yurochi and on three man-made islands along the shallow reef between Yurochi and Namu. The , ‘ locations from GZ were selected at such range distances (20,500, 24,000, 29,000, and 36,000 ft) as to produce expected degrees of damage ranging from severe to moderate deformation. , Because of a gross bombing error for the airburst of the eammicalalion all structures were subjected to pressures higher than expected and suffered complete collapse; therefore, the planned gradation of damage was not achieved. However, a qualitative demonstration of the effectiveness of the long duration positive blast phase was achieved, since one drag structure col- lapsed at a lower overpressure than that which an identical structure on Operation Teapot received without collapse. This agrees with theoretical studies which have indicated that, for drag-type targets, as the length of the positive phase of the blast wave increases, the overpressure required to cause a given degree of damage decreases. Analytical studies will be made of the test results obtained during Redwing and Teapot in an effort to determine the magnitude of the bonus effect of the long duration of the positive phase. 2.1.4 Program 4, Biomedical Effects -“ The only project in this program was Project 4.1, Chorioretinal Burns, by Air Force School of Aviation Medicine, Randolph Air Force Base, Texas. It was a sequel to a study in 1953 during Operation Upshot-Knothole. In the latter study, weapons of abo roduced burns in the eyes of rabbits at distances of 2 to 42.5 statute miles from GZ. On all studies prior to Operation Redwing, rabbits were the only experimental animals used to evaluate ocular damage. Four cases of accidental human burns were produced at distances of 2 to 10 statute miles. The present study was designed to furnish additional information on the requirements for protection against retinal burns, utilizing both rabbits and monkeys as experimental animals. The effectiveness of various parts of the power pulse was evaluated as to its ability to produce chorioretinal burns on rabbits and monkeys. This was accomplished by two series of time-fractionating shutters. The first group, open at time zero, closed at increasing intervals of time. The second series, closed at time zero, were open for preselected time increments during the flash. The feasibility of - 32 - 30