of major operational problems. Planning also looked more specifi- cally at another subject which had to be given early consideration— that of cryogenics. It was imperative that the sub-contractor in this field be acquainted with initial plans in order that CASTLE cryogenic and cryogenic transport requirements could be met on schedule. A third important subject considered was the matter of ‘cloud sampling. Though IVY roll-up plans had visualized the use for CASTLE of the IVY F-84G sampler aircraft, there were operational limitations in the use of this aircraft which the scientists wished as a matter of priority to overcome if at all possible. There was serious doubt at LASL that samples collected below 50,000 feet true altitude were representative of the materials contained in the main cloud. For this reason a number of conferences were held during this period for the specific purpose of determining what sampling techniques, both operational and scientific, might be devised. Considered as an allied matter was wnat type of bomb debris sample should be procured, It was essential that these re- quirements be defined early in order that Joint Chief's approval could be obtained if aircraft other than the F-84G's were to be utilized. In the meantime the criteria for manned aircraft to be used for sampling had been established jointly by LASL and AFSWC as follows; 1. Be multiplace to enable one person to fly while another operates the sampling devices and radiological instruments and acts as a sampling director. 2. Be multiengine for long range overwater flying safety. 39