2.4 MAJOR SCIENTIFIC CONSTRUCTION After it had been decided to use Bikini Atoll as an auxiliary test site, it was first necessary to set up an extensive horizontal control network covering all major islands of the atoll, Survey work was started early in the program and required a considerable amount of clearing on most of the islands as well as the establishment of a control point on a coral head in the lagoon. Previous experience during Operation IVY with the 9000 ft. long plywood tunnel, which contained a controlled atmosphere for diagnostic measurements of the MIKE shot, led to a decision to use pipes to accomplish the same general purpose in Operation CASTLE. These pipes were 8-5/8" O.D. by 40 ft. long and were butt welded end-to-end to make up the following arrays: Namu, 12-pipe array, 7500 ft.; Eninman-Reere, two-pipe array, 5600 ft.; EberiruAomon, two-pipe array, 2700 ft. Precise survey work was required to align ee ey erieee cee aw, Figure 20. 12-pipe Array Under Construction - Namu 45