General Casey, who had served in the Korean War, was in command of the US 1st Cavalry Division at the time of his death.

Casey served in combat during the Korean War, commanding a 7th Infantry Division company in engagements including the Battle of Heartbreak Ridge, for which he received the Silver Star.

He served as the Chief of Staff of 2nd Brigade, 1st Air Cavalry Division, in South Vietnam, from September 1966 to October 1967.

While home on leave from serving in Vietnam, he was promoted to major general during a ceremony on April 30, 1970, at the Pentagon.

On July 7, 1970, he was killed in a helicopter crash in South Vietnam when the UH-1H Huey helicopter he was co-piloting hit a mountain due to poor weather near Bao Luc as he was en route to Cam Ranh to visit wounded troops, before they were transported to Japan for medical treatment.