Work started on Eastney on the construction of a barracks to house the Royal Marine Artillery Division in 1862. Before then the Artillery companies attached to Portsmouth Division had been stationed at Gun Wharf and Clarence Barracks in Old Portsmouth, but most of their training and equipment was at Fort Cumberland. In the move to Eastney, the musketry and gunnery training fields were retained while the large parade ground and eventually a gymnasium, theatre and drill shed, made the division self contained. Along the beach lines was a long curtain with two forts at either end mounting several guns. The construction of the main barrack block was completed in 1864 and the first detachment of men marched in at the end of that year. Occupation by the whole Artillery Division did not take place until 1867.

The barracks were extended and added to over the years and the nature and role of the Marines housed there changed. When the barracks closed in 1991, it was occupied by less than 200 men. Following closure, it was sold and many of the principle buildings were converted to  residential use.

By far the most prestigious building within the barracks is the Old Officers’ Mess, which is now occupied by the museum. The centre position of this lavish building contained the public rooms whilst the officers’ bedrooms were in the wings. The officers dined and held their receptions and dances in what is now the Mountbatten Room and, on formal occasions, the landing upstairs was used as a minstrels gallery. Next door was the billiard room and library, now respectively the Medal Room and Band Room. The building was used as an Officers’ Mess until 1973 when, due to a decline in numbers, it was closed. Two years later the Museum, which had started its life in 1958 in the Division School by the old barrack gate, moved in and has occupied it ever since.