Two of the Palmerston Forts in the Solent, Spitbank and Horse Sands.
The Palmerston Forts that encircle Portsmouth were built in response to the 1859 Royal Commission dealing with the perceived threat of a French invasion. The forts were intended to defend the Dockyard in Portsmouth. Construction was carried out by the Royal Engineers and civilian contractors (under Royal Engineer supervision). In addition to the newly constructed forts, extensive work was carried out on existing fortifications.
The Portsmouth defences can be split into four distinct groups of forts, comprising four sea forts built in the Solent, a group of forts on Portsea Island, a group of forts along Portsdown Hill overlooking Portsmouth, and a group of forts on the Gosport peninsula.
As well as these forts surrounding Portsmouth, further protection for Portsmouth was provided by additional Palmerston forts on the Isle of Wight.
Spitbank Fort or Spitsand Fort or Spit Sand Fort or simply Spit Fort is a sea fort built as a result of the 1859 Royal Commission. The fort is one of four built as part of the Palmerston Forts constructions. Located in the Solent, near Portsmouth, England, and is now a luxury hotel.
Horse Sand Fort is one of the larger Royal Commission sea forts in the Solent off Portsmouth, Hampshire, England. The fort is one of four built as part of the Palmerston Forts constructions. It is 200 feet (61 m) across, built between 1865 and 1880, with two floors and a basement and armour-plated all round.