samples were removed. ? However, only one of the three F6F drones returned with a usable sample ,4° Evaluation of CROSSROADS Sampling . The Manhattan Project scientists left no doubt they had received valuable information from the sampler drones during Operation CROSSROADS. Sampling papers from both shots were good, although only one B-17 and one F6F got samples on BAKER Shot, Subsequent chemical tests indicated that no fractionation had taken place. The rubber air bags, carried aboard the B-17 drone aircraftworked very well for collecting samples, They had been opened for about 30 seconds while in the cloud; and scooped up air and debris samples. However, technicians were unable to use these because ", . . we were unable to learn in time how to get the activities out of the bag without fractionation, #2 Finally, a B-29 tracked the atomic cloud in an attempt to sample if all other methods failed. On ABLE Shot the B-29 attempted a sample several hours after the shot, but the radiation intensity was barely detectable 3 After a look at the data back at Los Alamos, Mr. Rubinson made these recommendations for future attempts to sample nuclear clouds: If it is at all possible, samples should be collected by the drone air filter method. These were our most reliable samples, . . . It should also be important to try to collect a sample about 2); hours after shot, with precipitron on a B-29, in order to see if an accurate efficiency determination is feasible with such a sample, ce Operation SANDSTONE - The following spring, on 3 April 1947, the Tos Alamos Scientific 13 AFWLHO SWEH-2-003), wr