<p>After all bombing north of the DMZ had been halted on order of the Johnson Administration effective 1 November 1968, the North stepped up its infiltration of the South and soon the Trail was carrying more traffic than ever. Since there was no proscription against hitting that region, a new air campaign, Commando Hunt, began with the old objective: stopping the flow of supplies down the Trail. As a secondary objective, the campaign would further test the Igloo White system.
</p>
<p>Strikes for the latter purpose were designated Commando Bolt, and they differed in their pattern from the others. In the ISC an assessment officer monitored the activation of the sensors, looking for some recognizable pattern that was characteristic of the movement of troops, trucks or tanks. He would then call up from the computer a sketch of the particular section of the Trail where the sensors were being activated, and superimpose a display of the target movement on that sketch. When the target had been located and identified, a call was made to the Tactical Air Control Center (TACC), the strike dispatching unit. They would call on the necessary number of LORAN-equipped F-4Ds and transmit the coordinates of the target. The pilots entered those coordinates into the aircraft computer. The target data transmitted to the F-4D included the estimated time of arrival (ETA) at the desired mean point of impact (DMPI). The computer continued to monitor the sensor broadcasts and to calculate the position of the moving target, extrapolating continuously to estimate the DMPI and the ETA over it.
</p>
<p>The pilots followed the course indication from the LORAN equipment, and the ordnance was dropped automatically when the computer had the bomb ballistics, the aircraft flight path and motion, and the truck movement coordinated to come together at the impact point. And, just in case the precision was not as advertised—and it wasn't, initially—the F-4Ds were loaded with either fragmentation bombs or other wide-area munitions.
