Admiral John Locke Marx, C.B., M.V.O., D.S.O. (23 April, 1852 – 16 September, 1939) was an officer of the Royal Navy.
In 1874, Marx was awarded the Royal Humane Society's Bronze Medal.
Marx was promoted to the rank of Lieutenant with seniority of 22 December, 1874.
In 1877, Marx was awarded the Royal Humane Society's Silver Medal.
Marx was promoted to the rank of Commander with seniority of 31 December, 1888.
Marx was promoted to the rank of Captain on 30 June, 1895, aged forty three years, two months, and seven days.
He was appointed command of the armoured cruiser Hogue on 19 November, 1902.
On the occasion of the King's visit to Ireland Marx was appointed a Member of the Fourth Class of the Royal Victorian Order (M.V.O.) on 11 August, 1903.
He served as captain of battleship Mars from October 1904. A very unsatisfactory inspection of her in May of 1905 showed her machinery and engine rooms in sad condition. The ship's performance in the heavy gunlayer tests of that year were also noted as being "very unsatisfactory." Marx was superseded in command in October, 1905.
He was appointed a Naval Aide-de-Camp to the King dated 2 March, 1905, vice Egerton.
Marx commissioned the new battleship Dominion on 17 August 1905. In gun practice later that year, the 12-in guns were "fair", the 9.2-in guns "good", and 6-in guns "disappointing."
Marx was promoted to the rank of Rear-Admiral dated 8 March, 1906 and ceased his work as Aide de Camp that same day. He arrived home on 2 April.
In accordance with the provisions of the Order in Council of 8 December, 1903, he was placed on the Retired List dated 8 September, 1909.
Marx was promoted to the rank of Vice-Admiral on the Retired List on 22 July, 1910, and to Admiral on 4 June, 1913.