Alexander Neill, formerly a Surgeons' Mate, was promoted to Assistant Surgeon in 1824 
Assistant Surgeon Sybille 1828
He served as assistant surgeon on the Sybille> off the coast of Africa and then set up a hospital at Sierra Leone -
'On Thursday the Esk, Captain Purchas arrived in Portsmouth from the coast of Africa. The Esk left Sierra Leone on 5th January in company with the Sybille and the Black Joke. In running down the Coast, they captured a Spanish slave vessel with 175 negros. The merchant seamen at Sierra Leone had suffered much from sickness arising principally from the indiscretion of the Master actively employing their crew, without the precaution of providing awnings to the boats in the heat of the day.
The Surry of London had sent sixteen men to the Hospital set up at Sierra Leone, then under the charge of Mr. Alexander Neill, Assistant Surgeon of the Sybille, and on investigating the cause of their illness, Mr. Neill learnt that they had in a short space of time discharged a large cargo; that they had proceeded up the River to take in timber many exposed in the upper part of their bodies to the sun while the lower parts was immersed in water, whilst others were in the hold stowing away the timber, exposed to the damp and miasma. Mr. Neill was successful in his mode of treatment, and had been generally so, having on a former occasion restored to health, seven out of eight of another vessel's crew. The North Star and the Primrose were cruising in the Bight of Benin.' 
Alexander Neill was appointed to the Primrose> when he was invalided home on the St. Helena in 1830.
Copy of an Order from Captain Gordon, Senior Officer on the African Station, to Mr. A. Neill, Surgeon, invalided from His Majesty's Ship Primrose -
'You are hereby directed to proceed to England in the Schooner St. Helena, taking charge of such invalids as may be sent from the Squadron for a passage in that Vessel. Given under my hand, on board the Atholl, at Sierra Leone, the 30th April, .1830. (Signed) Alexander Gordon '.
Primrose Detained by Diana Frigate
The St. Helena having on board 11 Officers and Seamen invalided from His Majesty's Ships of War on the African Station as Passengers: this Vessel was captured on the 6th of July, by the Diana Frigate, on suspicion of being a Pirate, the Officers and Men grossly insulted, their side arms and pistols taken away, Lieutenant Warren kept three days a Prisoner on board the Diana, and the sick and invalid Seamen removed from under the care of Mr. O'Neill 
Alexander Neill was promoted to the position of surgeon on 27 October 1830.
Appointed to the Phoenix
In 1834 he was appointed Surgeon to the Phoenix steamer 
Alexander Neill was employed as surgeon superintendent on four convict ship voyages to Australia -
The Belfast News Letter of December 28, 1859 revealed the sad details behind the following inscription in Armoy Presbyterian cemetery: Here lieth the body of Alexander Neill, Surgeon Royal Navy, Coleraine who died 22nd June 1857 aged 58 years, also the body of his son Hugh who was drowned at Coleraine 26th December 1859 aged 22 years, Alexander Neill 22nd June 1857 Hugh Neill 26th December 1859. Melancholy Incident. – A telegram was received in Derry on Saturday, stating that a young gentleman named Neill, a solicitor’s apprentice in the town of Coleraine, was drowned when skating on the Brook Dam, in consequence of the breaking of the ice. After the above was in type, we received a communication from a correspondent in Coleraine, to the effect that Mr Neill lost his life in a praiseworthy attempt to save the lives of two young lads, named Russell and Clarke, who went down through the ice near to where he was standing at the time; and though Doctors Sharpe and Carson were prompt in their attendance, after they were taken out of the water, the three perished, all efforts to restore animation proving ineffectual. The sad occurrence has cast a gloom over the town of Coleraine. .
 Naval Promotions and Appointments, Caledonian Mercury 8 July 1824