suitability. In early 1952 a decision was made to employ the F-84G single- place fighter-bomber. This aircraft had an ejection seat, anti-G suit pro- visions, windshield defroster system, automatic fuel transfer system, and an inflight refueling system. 1951, First accepted by the Air Force in June it was considered a first-line combat aircraft (Reference 29). Six- teen of these aircraft were specially modified for IVY sampling operations under the supervision of the Air Materiel Command (Reference 29, p. 66). These aircraft received four new avionics systems, radiac instruments, and dual cloud-sampling systems. A filter was also installed in the cabin pressurization system to prevent nuclear cloud particulates from entering the cockpit. This con- sisted of a plastic bag mounted in the gun deck of the aircraft nose. The system was actuated by a trigger switch on the control stick enabling collection of gaseous samples for 10 to 20 seconds et seq). (Reference 29, Chapter 8 A second sampling system involved modifications to the wingtip fuel tanks for the purpose of collecting particulate matter in the nuclear clouds. A diagram of this wingtip system is shown in the inset of Fig- ure 23. The operation was fairly simple; the pilot could open the valve behind the air scoop to admit ram air through the scoop. This air passed through filter paper, where particulate matter was collected, and then was vented. An ion chamber was mounted in the tiptank as a sensor to measure radioactivity of the filter paper and indicated the amount of sample collected at any given time. Figure 23 also shows the major modifications made to these F-84G aircraft to include the four avionics systems: the ARA-~8 homing device, ARC-3 VHF radio transceiver, the APX-6 IFF transponder, and the F-5 autopilot. Note also the sampling probe on the nose, which fed to the snap-bag. In January 1953, shortly after Operation IVY was concluded, AFSWC representatives met with LASL representatives to discuss CASTLE sampling requirements (Reference 29, p. 94). The sampling project manager outlined 134 Toegd One of the two sampling systems was called a "Snap-bag."