Monument MPM1699 - Horse Sand Fort

The monument includes Horse Sand Fort, a circular 19th century Royal Commission sea fort lying in the Solent 3.6km south east of Southsea Castle. Horse Sand Fort was one of a chain of four sea forts in the Solent recommended by the Royal Commission on the Defence of the United Kingdom in 1860 and designed to protect Portsmouth dockyard from seaborne attack. Construction started in July 1861 but was suspended between 1862 and 1864. The fort was completed in spring 1880. Horse Sand Fort is circular in plan and includes sea bed foundation walls of 8 ton pre-cast concrete blocks with an inner and outer casing of masonry. At the sea bed the structure is 73m in overall diameter and the thickness of the walls is 18m. The area enclosed by the circular walls is filled with shingle capped with a slab of concrete 3m thick. Above this lies a basement divided radially into compartments for ammunition and stores and concentrically by three circular passages. The outermost, the bolt passage, was to allow additional armour to be bolted on the exterior of the fort. Inside this the magazine includes 24 shell stores and lifts opening off a circular central passage and 14 cartridge stores and lobbies off the inner passage. In the central core steps led down to a laundry, cookhouse, ablution room and coal store. At a later stage of the fort's development the outer ring of shell stores was blocked with concrete and the bolt passage filled with sand in order to increase protection for the magazine. Above the basement are two gun floors, each of which is fully armoured for its entire circumference. The lower floor includes the landing stage and entrance in addition to positions for 24 guns. To the rear of these and their associated powder serving rooms and occupying the central area of the fort are officers quarters. The upper floor has positions for 25 guns to the rear of which are powder serving rooms and soldiers' quarters. The central area of the fort at this level includes quarters for a lighthouse keeper and officers' servants. The roof originally supported a lighthouse, ventilators and chimneys. Position finding stations were added towards the end of the 19th century but were removed by 1909. Emplacements were then added for three 6 inch breach loading (BL) guns and later a fire control position, battery commander's post and naval signal station. The fort was later equipped with anti-aircraft searchlights and, for brief periods, anti-aircraft guns. The roof also suports the loading gantry. Originally it was intended that the five turrets would have been equipped with two 12 inch 35 ton rifled muzzle loader (RML) guns but these were never fitted for financial reasons. By 1882 it was proposed to fit 12 inch 43 ton BL guns in alternate casements on the vulnerable sides of the fort, with six pounder quick-firing guns in the spare casements. During 1886-1887 some of the armament began to be fitted and hydraulic machinery was installed to power operate the mountings for the 12 inch guns, together with hydraulic lifts, operated by multiple pulleys, to raise the cartridges and shells from the magazine. Most of the RML guns were removed by 1898, when two 6 inch BL guns on electrically operated mountings were fitted. These were not a success and were removed to be replaced by three 6 inch MkVII BL guns on a central pivot mounting by 1909. Subsequently the armament was reduced and the hydraulic machinery stripped out. The fort was armed during both World Wars, the last gun being removed in 1951. The navigation light together with its associated solar panels and railings are excluded from the scheduling, although the structures beneath it are included.

Historic England, The National Heritage List for England (Index). SPM35.