for the experiment related to various tower heights required that several tower types be investigated, The Structural Department, after considerable study, presented the J-Division tower representative with a choice of 250 or 300 foot square cross section, free-standing towers or 300 foot guyed towers triangular in cross section, Because of the saving in weight which meant less iron would be drawn into the radioactive cloud, the 300 foot guyed tower was selected, The triangular cross section cut down the cost of materials and erection. The guying was by means of three cables at- tached to the tower at the 275 foot level, and guy wires were anchored to a concrete block 275 feet out from the tower base. Viewed from above, the guys were separated by 120°, The triangular cross section was 20 feet between legs from the 25 foot to the 300 foot level, this being the small- est cross section that would’ allow the clearances required for the main hoist and the personnel lift. Below the 25 foot level, the legs were battered out 7 feet to give additional space inside the shaft. The house at the top of the tower was rectangular, 16 feet, 4 inches by 18 feet by 12 feet high; the center of the building was only 1 foot, 5-1/2 inches from being over the center of gravity of the triangular section, This. necessitated cantilevering about 4 feet of the house beyond the tower shaft, Above the house was an A-frame to hold the main hoist gear, which was also centered over the main hoist, which was 1 foot, 5-1/2 inches from center of gravity of the tower shaft. By placing the main hoist so near the tower's center of gravity, it was possible to distribute the forces from the primary moving loads almost equally to each of the three legs. The A-frame was placed 4 feet above the roof in order to permit all of the hoisting gear to clear the roof and thus be completely out of the house. In order to allow the main hotsting gear to pass through the house floor, three removable aluminum floor panels were used. The resulting opening was 7 feet square, The rail guides for the hoist stopped at the underside of the housing floor, The personnel skip was designed so that all cables were kept below the 300 foot level, the sheaves on the lift being beneath the lift floor. The lift entered the house via a trap door that raised by the roof of the lift cab. The hoisting drums and motors were located at ground level near the base of the tower, The two hoists utilized two part lines to give a mechanical advantage of 2, The skip hoist could be controlled from the ground, house, or lift. The speeds were automatically set and varied depending upon nearness to the ground or house. Safety devices were provided to stop the lift at the two ends of runs or in case a cable should break or a drum run free, A ladder extended the full height of the tower. The completed preliminary drawings were checked by a J-Division re- presentative on November 9, 1948, and were handcarried to Los Alamos for the Test Director's approval on November 15, 1948. Weights of the materials in the tower increments of 25 feet were fur- nished Los Alamos on November 24, 1948. Because of the importance of the towers to the tests, an outstanding consultant was asked to check the design; he completed this study and 9-129