Chapter 4 evaluates US tactical air power from 1967 to 1968. Over North Vietnam, the Rolling Thunder air interdiction campaign struggled to isolate NVA/VC forces. Simultaneously, a strategic bombing campaign could not coerce Hanoi to withdraw its support of the insurgency. The direct attack of the NVA/VC forces in South Vietnam proved more effective, with the ultimate test occurring near the demilitarized zone (DMZ) at the US Marine base at Khe Sanh. Here, the NVA massed two divisions hoping to overrun the marines to achieve a decisive victory as they had against the French in 1954 at Dien Bien Phu. Instead, the American combined arms campaign defeated the NVA. The massing of ground forces at Khe Sanh differed from the NVA’s previous tactics of dispersing and taking sanctuary in Laos and Cambodia. Such defensive measures had previously allowed the NVA/VC to survive but had also delayed plans to launch a General Offensive and General Uprising. When the NVA/VC finally commenced their offensive in early 1968, they failed militarily at Khe Sanh and, more broadly, in the Tet Offensive. However, more importantly, the North Vietnamese succeeded politically as American support for the war evaporated.