On March 31, (NORTH VIETNAM) He hoped once again to induce North Vietnam's leaders to return to the Paris peace table. Although Hanoi agreed to begin discussions, it continued to pour 22,000 troops into South Vietnam every month. So the U.S. doubled its air operations south of the 20th parallel, concentrating on enemy troops andsupplies crossing the DMZ. After several months of discussions at Paris, on Oct. 31 President Johnson ordered a complete halt of all air, naval, and military artillery bombardment of North Vietnam and the "Rolling Thunder" campaign came to an end. The enemy had a sanctuary at home as well as in Cambodia.  

Throughout 1968,  LAOS,  the Communists slowly advanced across the northern part of Laos, defeating Laotian forces time and time again. This success was achieved despite U.S. military advice and assistance, since U.S. ground forces could not participate in defensive operations without violating Laos' neutrality. 

ADSID III electronic seismic sensor, one of several types dropped by U.S. aircraft along enemy roads and pathways in SEA. It was essentially a radio transmitter that picked up ground vibrations made by enemy trucks and troop movements and transmitted these signals to a friendly intelligence center through an airplane flying overhead. By keeping a record of these transmissions, U.S. personnel were able to determine the rate of enemy activity in any particular area and order an air strike when it became sufficiently promising.

Siesmic sensors were designed to stick in the ground when dropped from an aircraft. Another type of detection was the acoustic sensor which transmitted the actual sound, not ground vibrations, made by enemy trucks and personnel. It was designed to hang from a tree by its parachute after the drop. The sensor program, known as Igloo White, went into operation along the Ho Chi  Minh Trail in December 1967.