14 JAN--This Day in US Military History

1968 – U.S. joint-service Operation Niagara is launched to support the U.S. Marine base at Khe Sanh.

The Khe Sanh base was the westernmost anchor of a series of combat bases and strongholds that stretched from the Cua Viet River on the coast of the South China Sea westward along Route 9 to the Laotian border. Intelligence sources revealed that the North Vietnamese Army was beginning to build up its forces in the area surrounding Khe Sanh.
Operation Niagara was a joint U.S. Air Force, Navy and Marine Corps air campaign launched in support of the marines manning the base. Using sensors installed along the nearby DMZ and reconnaissance flights to pinpoint targets, 24,000 tactical fighter-bomber sorties and 2,700 B-52 strategic bomber sorties were flown between the start of the operation and March 31, 1968, when it was terminated.
This airpower played a major role in the successful defense of Khe Sanh when it came under attack on January 21 and was subsequently besieged for 66 days until finally broken on April 7.

https://thisdayinusmilhist.wordpress.com/2014/01/14/january-14/