He was on the return of Officers of the Medical Department of the Navy promoted from Assistant-Surgeon to Surgeon on 20 July 1838 
He was appointed Surgeon to H.M.S. Phoenix in the Mediterranean on 14 August 1839. H.M.S. Phoenix, 609 tons, a steam vessel, was built in 1832. Robert F. Stopford was Commander. Charles Daniel was employed as Assistant Surgeon 
He was employed as Surgeon Superintendent on the convict ship Sir Robert Peel in 1845. The Sir Robert Peel departed London on 9 September 1844 and arrived in Van Diemen's Land on 26 December 1844.
John Arnold Mould was on the List of Surgeons of the Royal Navy fit for service in 1852.
He was on the List of Officers, Crew and Marines on board a vessel at Malta when the 1861 UK Census was taken. He gave his age as 54 and status married.
He was on the list of Deputy Inspectors General of Hospitals and Fleets Retired (28 July 1862)
He was listed in the Medical Register 1865 - Deputy Inspector General of Hospitals and Fleets. Qualifications Member Royal College Surgeons Eng. 1830.
John Mould's wife Anne, daughter of John Borlase of Castle Horneck, Penzance, Cornwall died at Myrtle Cottage, Paignton in 1849 
In the 1851 Census John Mould, age 44, resided at Stoke Damerel, Devon. Status widower. His brother Thomas age 35 (a dentist), sister Elizabeth age 32, sister Louisa age 27, daughters Sarah age 11 and Anne age 9 resided with him. Stated occupation: Surgeon R.N. half pay.
John's brother William Pattison Mould, age 44, was also a surgeon. In the 1851 census he resided at Plymstock, Devon. His wife Mary is 43 and they have daughters Fanny age 8 and Sarah age 1 and sons Pentland age 6 and William age 4.
John Arnold Mould died on 19th June 1878 at Plympton St. Mary, Co. Devon. Administration of his Personal Estate was granted to Captain William Mould, R.N. of Tonbridge Wells, Kent, brother of the deceased. 
 Hampshire Telegraph 30 July 1838)
 Royal Cornwall Gazette 2 February 1849
 Ancestry.com. England and Wales, National Probate Calendar (Index of Wills and Administrations), 1861-1941 [database on-line
 Haultain, C. (compiled), The New Navy List, 1840, p. 214