Fort Nelson, above Portsmouth

The 'Palmerston Forts' that encircle Portsmouth were built in response to the 1859 Royal Commission dealing with the threat of a French invasion.

Portsmouth Dockyard faced the new French Dockyard at Cherbourg only 81 miles away, constructed by the Emperor Napoleon III.

It was feared that a French invasion force might land along the Coast, occupy Portadown Hill and fire their new long-range guns to bombard Portsmouth down below. The French had launched in 1859 the first ocean-going ironclad warship, the wooden-hulled Gloire. In response the Royal Navy built the first ironclad war ships, HMS Black Prince and HMS Warrior now docked in Portsmouth and blipped earlier in this series.

The forts were built to defend the Dockyard in Portsmouth. Construction was carried out by the Royal Engineers and civilian contractors (under Royal Engineer supervision).

As well as the forts surrounding Portsmouth, further protection for Portsmouth was provided by existing and new defences on the Isle of Wight. The Portsmouth defences form a massive series of four distinct groups:

Gosport group
Portsea group
4 forts in the Solent; and
5 forts on Portsdown Hill and 2 redoubts

Fort Nelson is one of the Portsdown Hill forts.

By the time the Palmerston forts were completed in 1871, France had been defeated by Prussia in 1870. The forts had a cost a fortune to build and soon became known as 'Palmeston's Folly'.

Today it is an outpost of the Royal Armouries.