Airblast was measured at distances of 2000 to 61,000 feet from a detonation of four million pounds of ammonium nitrate. The charge was horizontally dispersed in three vertical layers. The top layer contained 0.596 million pounds; the second, 160 feet below, contained 2.119 million pounds and was detonated 87 msec after the first; the third, 100 feet below the second, had 1.285 million pounds and was detonated 144 msec after the first. Attempts to reproduce measured ground-shock-induced peak overpressure using results of previous single, row, and array-charge explosions showed best agreement with the equivalent row-charge analogy, which produced 80 percent of measured values.