search and destroy missions and of body counts, which affected the O/B numbers. A significant benchmark of success was the cross-over point, achieved when the prevailing army wears down an enemy until he begins to suffer casualties at a rate higher than he can replace. This carnage allows the expectant victor to see "light at the end of the tunnel". The war ends, eventually, when the losing side can no longer field sufficient forces to sustain the fight. Yet the metrics of replacement, from existing reserves, new recruitment, or infiltration from outside, were debatable. For President Johnson, favorable changes in the O/B numbers for the VC, such as reduction in the number of their main force, would directly indicate the war's progress. American combat forces were introduced in 1965. Their numbers were steadily augmented until reaching over half a million troops. Military doctrines generally had required a ten to one advantage to defeat a guerrilla 'people's army'. Yet because American technology provided better mobility (e.g., helicopters) and increased firepower in weaponry, a mere three to one ratio was thought sufficient. General Westmoreland mentioned the possibility of reaching a cross-over point ahead. A war of attrition was one of several conventional military approaches. Yet in Vietnam a revolutionary situation existed, a civil war whose combatants were not only regular soldiers but also part-time guerrillas who were civilians by day. The fighting was largely without borders as control of much of the country was openly contested. A conventional conquest of territory was seldom an option. The 'search and destroy' operation, a tactic used by American forces to attrit the enemy, was difficult as the VC resisted detection; merely finding such an elusive enemy was a major problem. An entirely different approach was counterinsurgency, a strategy in which protection (pacification) of the population was a prime objective. After the 1968 Tet offensive, this latter approach was given much more emphasis. In the meantime, for the American military in the mid-1960s, attrition strategy generally governed the way the war was fought. Institutional context The O/B controversy attracted the interests of powerful institutions in the federal government. In such a climate, an intelligence agency became vulnerable to pressures tending to influence, or compromise, its finished product. Consequently, the intelligence community as a whole, including military intelligence and the CIA in particular, had to chart a course through a maze of national policy, administration agendas, demanding