Mariner artillery suggests a royal navy role, as does the address on portsea island (better known as Portsmouth and Southsea, home of a naval dockyard and marines barracks). you may be able to find records of him in the ships musters at the national archives ( nationalarchives.gov.uk) probably on the file ADM 38, but you would need to know the name of the ship he served on, as the files are indexed by ship, not by personal names. also it might be worth looking at the pension records for widows and orphans of commissioned officers, which can be found at the national archives (also in the ADM series of files). A good book to get information on what is held in the national archives is 'tracing your ancestors in the national archives' by amanda bevan, isbn 1-903365-89-9, chapter 28 covers naval records. I appreciate though that kew is a fair way from where you are, but maybe there is someone who could look at the records on your behalf.
do you know anything of his ancestry?, if he has a link to the Dyer families of Minchinhamton (Gloucestershire) or Bristol he may be one of my distant relatives too.