Admiral Sir William Donough O'Brien (13 November 1916 – 19 February 2016) was a British military leader.
He was the Commander-in-Chief of the Western Fleet.
He was then appointed Naval Secretary in 1964.
He was appointed Flag Officer Aircraft Carriers in 1966, Commander-in-Chief of the Far East Fleet in 1967 and Commander-in-Chief of the Western Fleet in 1970.
He retired in 1971.

O'Brien died on 19 February 2016 from complications of pneumonia.
He had also been suffering from Alzheimer's disease.
He was 99.
Admiral Sir William Donough O'Brien (13 November 1916 – 19 February 2016) was a British military leader. He was the Commander-in-Chief of the Western Fleet. He was then appointed Naval Secretary in 1964. He was appointed Flag Officer Aircraft Carriers in 1966, Commander-in-Chief of the Far East Fleet in 1967 and Commander-in-Chief of the Western Fleet in 1970. He retired in 1971.
O'Brien died on 19 February 2016 from complications of pneumonia. He had also been suffering from Alzheimer's disease. He was 99.
William O'Brien (Royal Navy officer)