This manual describes the use and structure of the June 30, 1976 version of the Four-D propagation code for high energy laser beams. It provides selected sample output from a typical run and from several debug runs. The Four-D code now includes the important noncoplanar scenario feature. Many problems that required excessive computer time can now be meaningfully simulated as steady-state noncoplanar problems with short run times.

The objective of this investigation is to determine the upper limits on the thermal yield of a 1 kt source detonated at shallow depths. Three problems were computed for the depths of burial of 0.5, 1.5, and 3 m. The source is an iron bubble with 30 cm radius and 25 kg of mass. The computation was done on the CEL code. The results show that the relative thermal yield is no more than 6 percent, and that it vanishes at DOB of about 4 m. The computed blast strength is plotted against the range. The results are consistent with the measurements on ''Johnnie Boy'' and ''Jangle-U'', and in good agreement with the RAD9 calculations and the HULL calculations.