It was largely based on a tactic known as "Search and Destroy"

This was first implemented at the Battle of Ia Drang Valley, in which Air cavalry flew into a zone of suspected enemy activity on helicopters, secured a landing zone in which constant resupply, reinforcement, and medical evac could be continually performed.

The idea of Search and Destroy was to find the Vietcong (early war) and kill them. General Westmoreland wanted body counts of dead enemy that would prove that the guerilla war was being won.

There were major battles involving US outposts, the most famous being Khe Sanh. This was a very large US outpost in a strategically important area that threatened the effectiveness of the Ho Chi Minh trail into Vietnam. The US defense at Khe Sanh was similar to that of Dien Bien Phu, which in 1954 was the sight of a major French outpost that was sieged and after a very bloody battle, resulted in a Vietnamese victory over the French. The main issue at Dien Bien Phu was the airstrip inside the fortress. The French used airplanes to land supplies and reinforcements which became problematic when the Vietnamese were able to bombard it with artillery and mortar fire. The airstrip became too damaged for aircraft to land, forcing them to make desperate and inaccurate paradrops of troops and supplies, and they were also consequently unable to evacuate the wounded.

The US strategy at Khe Sanh drew upon the mistakes made by the French at Dien Bien Phu. Instead of resupplying via airplanes, they used helicopters which ensured a continuous resupply and rapid deployment of soldiers where needed. The main concern was being overrun at any point in the combat base, so the rapid deployment of soldiers was vital to plugging any holes that developed in the lines.

I've written more extensively on the US strategy in the Vietnam War in this post.