During the halt in the bombing campaign against North Vietnam (in force from 1968 until the early 1970s), TOPGUN established itself as a center of excellence in fighter doctrine, tactics, and training. By the time aerial activity over the North resumed, most Navy squadrons had a TOPGUN graduate. According to the USN, the results were dramatic. The Navy kill-to-loss ratio against the North Vietnamese Air Force (NVAF) MiGs soared from 2.42:1 to 12.5:1, while the Air Force, which had not implemented a similar training program, actually had its kill ratio worsen for a time after the resumption of bombing, according to Benjamin Lambeth's "The Transformation of American Airpower."