Route Pack 6, or 6B specifically, referred to the area around Hanoi and was considered to be the best defended airspace in the world at that time, and home to the dreaded Thud Ridge.

Early during the Vietnam War, the Air Force and the Navy found it difficult to conduct joint operations, and instead competed for resources and targets.

As a result, an Air Force-Navy coordinating team met in December 1965 and divided North Vietnam into six sectors.

The Navy's Carrier Task Force 77 handled operations in RPs 2, 3, 4, and 6B, as these bordered on the Gulf of Tonkin.

The bombing halt allowed the defenders to rationalize and improve their system, which eventually included 200 SA-2 sites around the country and along the Ho Chi Minh trail.