Question

What was the 1968 offensive launched by the North Vietnamese against the South Vietnamese called?

Answer 1

The Tet Offensive.

Explanation:

Launched on 30th of January of 1968, the Tet offensive was one of the major engagement of the Viet-Nam War.
Using the lull in the operation during the celebrations of the Tet (Vietnamese New Year) the North Vietnamese Army supported by the Vietcong attacked along the entire South Vietnam even striking the American Embassy in Saigon and sieging the imperial city of Hué.

At the start the offensive seemed to be successful but soon the weight of the military hardware (tanks, aircrafts and artillery) and training in large scale and open field conventional fighting of the US army took the upper hand.

The North Vietnamese Army had to retreat while the Vietcong had to go back into hiding (not without extracting retaliations on local "socially undesirable" persons).