Because of a subsequent decision not to use this tower at the Prov- ing Ground, the purchase order was cancelled on August 24, 1950. October 12, 1950, the work was reinstated, On On December 7, 1950, AEC requested that the tower be rushed to completion and forwarded to an AEC storage yard for holding until required by the AKC. 200 FOOT TOWERS Characteristic of the rapid scientific advances that produced engineering challenges throughout the Project was LASL's request, nineteen months after tower design had started, that H & N design a 200 foot tower capable of supporting 200 tons. This was an entirely different type of tower, requiring a completely new analysis and design. Speed, both in design work and procurement, was essential in order to have towers of this new type erected at the Proving Grounds in time for tests early in 1951. This change in test objectives, although made late in the period of design and construction, did not relieve the date established for completion of all facilities, Careful coordination of design, procurement, fabrication, transportation and construction made possible this unprecedented accomplishment. Chronologically, this assignment was handled as follows: Cn April 27, 1950, official authority was given to the design group, and on April 28, a preliminary drawing based on J-Division's telephone call was submitted to J-Division. The preliminary design was approved on May 3, 1950. Because of the loads involved and the desire to keep the tower weight as low as possible, the use of silicon steel for the legs was approved. The design of the tower was complicated by the large amount of scientific gear that occupied a large portion of the space within the tower shaft, i.e., the NRLK coax- jal cables and their special shielding and the UCRL vacuum pipes that had to be held to close tolerances. The inclusion of the User's equipment made it necessary to place the main hoist and the skip hoist outside of the tower shaft. Because of the eccentric loading, this complicated the design. In addition, the house on top was equipped with a standard industrial traveling bridge crane, which could develop some large lateral forces as well as impact forces. When authorization was given to design a tower according to the new criteria, it had not yet been decided how many towers of this de- sign would be required or what to do with the 300 foot aluminum tower which was being fabricated. However, due to the short time available the decision was quickly made to procure three towers of the new design plus a 25 foot top section and house to be shipped to Los Alamos as a mock-up. Consequently bids were taken on a price per pound of steel basis, using the preliminary sketch as a bidding drawing, The contract was awarded to Union Iron and Steel Co. on May 12, 1950, the bid being $ 0.097 per pound. To save the time usually required to get the large beams needed in the floors, the use of 36-inch deep beams salvaged from an old 57140