because of yield might not be acceptable if fired from a 300-foot tower might be scheduled atop a 500-foot tower or in a balloon cab. In a surface or shallow underground shot, a device of very limited yield is required so offsite fallout may be held within fully acceptable limits. \ Some devices must be fired in a stable Placement of Devices. position, so precise measurements may be obtained by instruments registered on an exact point. Such devices are fired in Nevada on towers, ranging from 300 to 500 feet or higher in altitude. Where only fair precision is required, it has now been determined that a device may be fired in a balloon cab, where some motion may always be expected. Where only general positioning is required, an air drop may be scheduled. For some studies, surface and shallow underground positioning of shot devices may be called for, Elimination of all radioactive fallout through deep underground positioning of devices with small yields is another possible method, Placement, to Avoid Contaminating Another Site. Sometimes a device must be detonated near the site of a future shot. Care must be taken that positioning of the device is such that winds at shot time will not place heavy concentrations of radioactive fallout on the future site so as to make it unusable, Hours of Tests. Technical requirements determine whether a shot may be fired in daytime or requires darkness. If daylight is permissible, the usual hour is about 9:30 A.M., when wind usually is the calmest of the day. Experiments involving photography usually require darkness. For this reason the immediate pre-dawn hours are used, when there is sufficient darkness for experiments, followed shortly by daylight to facilitate post-shot operations. The wind also is usually calm at this period. A majority of shots in Nevada is fired before dawn. Division of Real Estate, and of Air. The ground firing area around an air-drop zero point or a tower site is a fairly extensive piece of desert real estate, but with the use of tests for many pur- poses other than nuclear diagnostic experiments, there has developed a considerable problem of space. Complicating the problem is the fact that a majority of the experiments must be upwind from the detonation to avoid radioactive fallout contamination. To meet the problem the ground is divided into sectors such as a diagnostic sector, civil and military effects sectors, military materiel sector, and perhaps sectors for observation and maneuver by participating troops, and for a Civil Defense exercise. The air above the Test Site must be divided as carefully. Well over 100 aircraft may be employed on a single test, with functions varying from dropping a bomb to tracking the radioactive cloud for hundreds of miles. With so many aircraft involved, schedules, orbits and abort procedures must be pre-planned to fractions of seconds, . COP zy 7: Lay ag OB .