Henry Priaulx Cayley was born in Clifton, Gloucestershire on 29th December 1877. He was a son of Henry Cayley, surgeon major in the Indian Medical Service, and his wife Letitia Mary Walters.
Educated at Eastman's Naval Academy, he joined the Royal Navy's training ship Britannia in 1891 as a cadet and was promoted midshipman in 1893 and sub-lieutenant in 1897. His early sea-going appointments were to the Mediterranean Station and the Channel Fleet; then in 1899, after being commissioned lieutenant, he served on HMS Undaunted during the Boxer Rebellion. He continued to serve in the Royal Navy until 1912.
On 14th July 1906 he married Ethel Mary Hewitt in Kensington, London.
In 1909 Cayley, now a Lieutenant, was posted to the Australian Station as the Royal Navy's inspector of warlike stores. To take advantage of better career opportunities, he resigned in mid-1912 and joined the newly established Royal Australian Navy, retaining the position of inspector of warlike stores. When war broke out in 1914 he was made an acting Commander and sailed with the first Australian convoy as transport officer on the troopship Euripides. He was transferred to HMS Isis in January 1915 and made substantive Commander in April. In March 1917 he was appointed second-in-command to Captain John Dumaresq in HMAS Sydney, then carrying out patrol and convoy duties in the North Sea.
He was promoted Captain on 1st April 1919 and took command of the Sydney. In June, when the Sydney was returning home, Cayley was asked to help quell civil riots in the Straits Settlements. He promptly supplied landing parties at Singapore and Penang. In November the Sydney grounded (without damage) at Townsville, Queensland. Cayley and his navigating officer were court-martialled and reprimanded for negligence; the findings against the navigator were quashed on appeal, but those against Cayley were confirmed - he was held solely responsible for the incident. He retained the confidence of Dumaresq, who was then Commodore commanding the Australian Fleet, and the mishap does not appear to have prejudiced his chances of preferment. In 1925 he was appointed second naval member, one of the few RAN men to serve before 1939 on the Australian Naval Board. In May 1927 he became commander of HMAS Melbourne, then in October was made captain superintendent in Sydney.
He was posted back to London in 1929 as naval representative on the Australian High Commissioner's staff but, when his position was retrenched during Depression cuts, he retired on 7th August 1931 in the rank of Rear Admiral.
He spent the rest of his life in England, and devoted himself to Christian Science, the study of which had led him to abandon the Catholic faith and to become a teetotaller. Survived by his son, he died of pulmonary embolism on 31st December 1942 at his home in Chelsea.
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