 The B-52 cells (groups of 3 aircraft) were guided onto these boxes by ground-based radar.During May 11 and 12, the U.S. Air Force managed an "Arc Light" mission every 55 minutes for 30 hours straight—using 170 B-52s and smashing whole regiments of PAVN in the process.Despite this air support, the PAVN made gains, and were within a few hundred meters of the ARVN 5th Division command post.