kiloton thermonuclear device left a crater 1,280 feet across and 320 feet deep. Again radioactivity was detected off-site. Shot ANACOSTIA was a low-yield device development test on 27 November 1962. No radioactivity was detected beyond the boundaries of the Test Site.
Two other Plowshare cratering tests were scheduled for 1969. The shots, code named YAWL and STURTEVANT, were planned for detonation on northern Yucca Flat. In preparation for the tests, DOE officials analyzed the predicted effects that the blasts would have on Area 51. Documents titled EVENT SAFETY AND DAMAGE EVALUATION - AREA 51 for each test are available at the DOE Public Reading Facility in Las Vegas. These draft reports provide insight into the manner in which nuclear testing impacted operations at Area 51. The analyses for both shots cover the following areas: predicted effects, atmospheric overpressures, radiation, base surge and ejecta, possible damage to Groom Lake road, evacuation from Area 51, and possible delays in firing.
According to the documents, the STURTEVANT device was to be buried about 800 feet below ground, and have a yield of 170 to 250 kilotons. YAWL was to have a yield of 750 to 900 kilotons. Buried about 1,000 feet underground, YAWL would have blasted a crater 500 to 700 feet deep and as much as 1,500 feet across. Predicted effects of both shots were similar. "Anticipated ground motion at Area 51 Camp," according to the STURTEVANT report, "is below the damage threshold for structures, therefore, only minimal architectural damage is expected."
Radiation was an important consideration. Neither shot would have been fired if winds would cause the "hot line", area of highest radiation, to pass near the airbase. The reports state that "wind conditions at detonation time will be chosen such that predicted contamination at Area 51 camp will be less than 6R total dose including shine and redistribution. The dose rate is expected to fall below 6mR/hr before D+4." To reduce risk of radiation exposure, personnel were to be evacuated as with so many previous shots. "Detonation...will require evacuation of the entire Area 51 on D-day." Additionally, the duration of the evacuation would "depend on reliability of contamination predictions and in-field measurements. Re-occupancy is expected by D+4 although field conditions may require short work shifts for several days, possibly two to three weeks."
The possibility of successive firing delays raised the specter of evacuation for a period of days, or even weeks. As always, weather was the determining factor. The reports specified that it might "be necessary to delay detonation on a day-to-day basis awaiting favorable atmospheric conditions." In the case of YAWL and STURTEVANT, all the planning was in vain. Both shots were cancelled.