A technical article in the journal of the IRE (Institute of Radio Engineers) Professional Group on Military Electronics in February 1961 "A High-Resolution Radar Combat-Intelligence System", L. J. Cutrona, W. E. Vivian, E. N. Leith, and G. O Hall; IRE Transactions on Military Electronics, April 1961, pp 127–131 described the SAR principle and both the C-46 and AN/UPD-1 versions, but did not tell how the data were processed, nor that the UPD-1's maximum resolution capability was about 50 feet .