BARREL ROLL was the US air campaign conducted over northern Laos in support of the Royal Lao Government (RLG). Although the campaign supported US national policy in Southeast Asia (SEA), it was constrained by US military strategy and objectives in South Vietnam and responded to North Vietnamese military strategy and objectives. The mission of BARREL ROLL was to conduct air operations in support of the RLG by: (1) the interdiction of enemy supplies moving through northern Laos, and (2) providing air support for Laotian ground forces fighting the North Vietnamese and Pathet Lao. The last four years of BARREL ROLL--November 1968 to February 1973--are especially interesting due to changes in US national and military strategy in SEA. Examination of air operations uses the "campaign model" found in Department of Defense Joint Publication 3-0, Doctrine for Joint Operations, and answers five questions: (1) Why is the campaign conducted; (2) What is to be accomplished; (3) How will it be accomplished; (4) How much resource is applied; and, (5) What were the results. Results are assessed in terms of effects and effectiveness of airpower. Effects are the direct or immediate outcome, for example, the destruction of a target. Effectiveness examines the indirect outcome at the operational or strategic level, for example, defeating the enemy in battle or achievement of theater objectives. From the perspective of achieving objectives, BARREL ROLL was an effective air campaign in support of national, strategic, and operational objectives in SEA. Relevant lessons of BARREL ROLL are the central control of airpower, the employment of airpower in an undeveloped country, and use of airpower in unconventional combat. Cost is assessed in terms of attack sorties, ordnance delivered, and bomb damage assessment results. These data are provided in an appendix.