John Joseph Timothy Hennessey[1] (20 August 1921 – 20 March 2001) was a United States Army four-star general who served as Commander in Chief, United States Readiness Command (USCINCRED) from 1974 to 1979.

After attending Saint Mary's University of Minnesota for three years, Hennessey enrolled in the United States Military Academy and graduated in 1944, receiving his commission in the infantry.

When the 11th Air Assault Division was converted to the 1st Cavalry Division (Air Mobile) in 1965, he accompanied that unit to Vietnam as executive officer of the 1st Brigade, later becoming brigade commander after being promoted to full colonel.

On 4 August 1967 the Chief of Staff of the United States Army established the Task Group on Army Preparedness in Civil Disturbance Matters chaired by Hennessey from the Office of the Deputy Chief of Staff for Military Operations, the work of this task group was conducted largely by field grade officers and was probably the most comprehensive study of the Army's civil disturbance mission ever conducted.

His awards and decorations include the Defense Distinguished Service Medal, the Army Distinguished Service Medal, Legion of Merit with Oak Leaf Cluster, the Bronze Star with "V" and three Oak Leaf Clusters, the Air Medal with four Oak Leaf Clusters, the Combat Infantryman Badge, Army Aviator Badge and Master Parachutist badge.