His first assignment was as a beat patrolman attached to the
Potrero station. In 1943, he was transferred to the Accident Investigation Bureau and, in 1946, he joined the bureau of inspectors. A year later, he was assigned to the
Homicide Detail. His partner during his assignment to homicide was Inspector Francis J. Ahern. Cahill, in an interview with local San Francisco media shortly before his death, claimed his relationship with Mayor John F. Shelley was broken by the
Summer of Love in 1967: "Jack Shelley, (a Democrat, former liberal congressman and labor leader), did not want to show a heavy hand toward the
Hippie &
Flower Children element." When hippies flooded
Golden Gate Park and the
Haight-Ashbury district, Cahill contacted the new California governor,
Ronald Reagan, for the
California Highway Patrol and the
California National Guard to enter San Francisco and sweep the hippies from the city. By law, Reagan needed a request from Shelley. Reagan and Cahill pleaded for his signature, Shelley refused. On a national level, Cahill was one of the more well-known city police chiefs. He was the only police chief to be selected by
Lyndon Johnson to serve on the
President's Commission on Law Enforcement, in 1965. He impressed FBI Director
J. Edgar Hoover, who called him the best public administrator in the entire US, so much that Cahill was one of the two finalists (along with
Clarence M. Kelly) for the FBI Director post. He was the only police chief in the country to be on the acclaimed television program,
Meet the Press, and his discernment and articulateness struck everyone, when he appeared as a panelist on February 19, 1967. Cahill retired from the force on February 4, 1970, after a request from Mayor Joseph Alioto, who later appointed Alfred Nelder as San Francisco Police Chief. Alioto felt Cahill was too "rigid" and "old fashioned" for law enforcement in 1970s San Francisco. After Cahill's retirement, he became chief of security for Pac Bell in San Francisco until July 1, 1975, shortly after he reached the mandatory retirement age. He also won a position on the San Francisco Charter Revision Committee. == Later life ==