bridge in the Los Angeles area was sanctioned. As the design progressed the steel fabricator was able to stockpile more of the material he needed. From May 19, 1950, until the time of the test, these towers were constantly undergoing changes. Each change of tower loading or requirement came in separately and required many reanalyses and new drawings. An illustration of the magnitude of these revisions is shown by the fact that although only 9 drawings were required to show the structural portion of the shaft and house at the time fabrication began, by the time the towers were erected, 16 more full size drawings had been added to depict the changes. A few of the major revisions are as follows. Limonite inside the house was changed to lead on May 19. On June 23, the original size of the house was changed from 20 feet by 20 feet by 12 feet to 20 feet by 29 feet by 164 feet. One tower was to be provided with a special 9 foot by 7 foot overhanging platform capable of supporting 4 tons. UCRL's vacuum pipes and NRLK's limonite column, which are described more fully later, were never really firnmed up. The vacuum pipes had to be lead-shielded at different levels; therefore special supports were needed. The lead-limonite column that was first proposed to shield the NRLK coax cable from the ground into the house at the top, a vertical distance of 200 feet, was originally 4 feet in diameter, Later the lead~limonite concrete was discarded in favor of a lead column 3 feet in diameter. This necessitated changing some of the interior bracing. Prior to this change, it had been necessary to build sufficient inherent strength into the tower shaft to carry the construction loads that would be imposed during the building of the column. This required close coordination with the Holmes & Narver construction forces. In order to satisfy the initial requirements, a four leg, guyed tower 200 feet high to the underside of the floor of the house at the top was selected, The shaft of the tower was 20 feet square at all elevations, Eight guys were provided at the 175 foot level. A summation of all loads involved at the base of the tower indicated a load of approximately 2100 tons. To keep the soil pressure within 3000 pounds per square foot would have required a foundation mat approximately 40 feet square. However, because of the sequence of construction of the heavy units comprising this total load, the foundation mat would be subjected to nonconcentric loading which would have involved unequal soil loading, resulting in possible tilting of the mat out of a true horizontal plane. This, in turn, would have induced unknown loads into the tower shaft, which would be securely guyed in a vertical position, This necessitated sending a foundation consultant to the Proving Ground to investigate the foundation conditions at the tower sites. The firm of Dames and Moore, a nationally recognized firm of soils consultants, had been used by H & N to analyze the soil samples obtained by the reconnaissance group. In connection with this work several of the key personnel had been "Q" cleared, so it was possible to send a recognized soils expert to the Jobsite immediately. d~141