On this date: May 20, 1969

Hamburger Hill.

United States and South Vietnamese forces captured Hamburger Hill. Among others, the 101st Airborne was involved. While the battle may not have been well considered, or planned casualties were actually not exceptionally high.  However, the impression back home was one of the early turning points in the support for the war.

From History in Film, the intro to the description of the 20th of May.  The entire battle can be found on the site.

For two hours, beginning around dawn, the air force jet and Skyraider pilots bombed all four sides of Ap Bia with every type of armament they could "scarf up" at their bases. Like the sequence of the previous ten days, when the pairs of planes left the area, the artillery blasted the NVA positions with tons of 105mm, 155mm, and 8-inch artillery rounds. At 1000, the four infantry battalions assaulted the burning, scoured, denuded mountaintop. In 3/187th area, the lineup had A Company on the right, C Company in the center, and A/2/506th on the left. When the troops reached the base of the mountain, they formed long skirmish lines and began to move cautiously up the slopes. They were surprised when they were not fired on with the usual heavy bursts of fire at close range.

The whole battle's history is worth reading.  If you have the time you can start here.  The whole battle was actually from May 10th through the 20th.