Crater depth as shown in the profile is 171 feet, Figure 19. It should be pointed out that the data is taken from lead-line soundings since fathometer surveys of this crater 4 days after shot time indicated a depth of only 81 feet. The difference between lead-line and fathometer surveys was presumably due to a suspension of mud and silt in the crater. The scaled crater radius of 179 feet for an actual radius of 2,000 feet, or at the most con- servative estimate, 164 feet for a radius of 1,825 feet, is the largest measured scaled radius from a land surface shot. Using a washing factor of two and considering Shot Koa to be a normal surface burst the scaled radius value calculated from TM 23-200 would have been only 128 feet or a factor of 30 to 40 percent lower than the actual value. The scaled crater depth of Shot Koa was 28.5 feet. The scaled depth value obtained using the TM dry soil curves and a washing factor of 0.7 was only 14 feet. Soil information obtained at Sites Gene and Helen, indicated soft sand with fractured underlying lens of cemented sand. The fractured condition may be partly due to the shattering effect of the nearby Ivy Mike and Operation Redwing Shot Seminole shots. During past operations large, waterfilled voids were found in the soil underlying Sites Gene and Helen. Two such cavities vented to the surface close to the crater and can be Seen in Figure 17. Available information indicated that the soil condition in the Shot Koa area had somewhat less strength than that at Site Yvonne and was probably more fractured than NTS soil. This fractured condition may have accounted partly for the large crater size of Shot Koa, and some thought might be given to introducing a fracture factor, similar to the strength factor used in the Shot Cactus correlation. However, since no data exists to show the difference in crater size that could be expected from fractured soil, such a factor is not used. The only apparent unique feature of Shot Koa was the water tank in which the device was detonated, Figure 7. It was desirable to determine if there were any data which might indicate that the water tank produced any unexpected effects. Fireball photography showed a somewhat aspherical shape as late as 2.5 msec after the detonation, corresponding to a fireball radius of 150 meters. The time to minimum, as indicated by the bhangmeters, was about 35 percent lower than would have been expected on the basis of the fireball yield determination. Since no other unusual conditions were evident as contributing to the large crater size, it was concluded that an increased coupling of energy into the ground was brought about by the water tank surrounding the Shot Koa device. The water tank had, -therefore, affected the early fireball or shock transport history of the nuclear detonation from its normal pattern of an airground interface shot. This may have been due to thefact that in an air-ground interface detonation there is a tremendous difference in density between air and ground. Thefireball had encompassed a large area of the ground surface but had gone only a short distance into the ground by the time of hydrodynamic separation. When the device is enclosed in a water tank there is less difference in density between the water-ground interface, permitting the energy to be transported more nearly equally in all directions until the water-air interface is reached. The effects of the fireball history are more meaningful if it is realized that for a nuclear detonation at an airground interface less than 1 percent of the total yield contributes to the formation of the crater. A relatively small influence on the overall energy partition could have a large effect on the crater formation mechanism. From a comparison of the above values withITM23-200 it can be assumed that the water has acted as a tamping device to increase the coupling of energy to the soil. 30 It would appear that