Royal Commission on the Defence of the United Kingdom

In 1859 Lord Palmerston instigated the Royal Commission on the Defence of the United Kingdom because of serious concerns that France might attempt to invade the UK. The recent period had seen great improvements in gunnery (with RML and RBL designs); the widespread introduction of steam propulsion in ships (the French La Gloire and British response HMS Warrior are examples); and the growth of the French battle fleet (between 1854-1858 it had achieved numerical equality to the British). These factors convinced him that Britain's coastal defences were inadequate to prevent invasion by Napoleon III if the Royal Navy were lured elsewhere.

The Commission consisted of six eminent naval and military officers, plus a civilian representative of the Treasury, James Fergusson, who in 1856-57 had published papers warning of the vulnerability of Portsmouth. Its brief was to enquire into the state and sufficiency of fortifications existing and planned for defending the UK, with a specific focus on naval dockyards.

They concluded in their report in February 1860 that the fleet, standing army and volunteer forces, even combined, did not provide sufficient defence. An intensive program of fortification was begun; the designs being overseen by Major William Jervois of the Royal Engineers, who was secretary to the Commission. The Commission recommended that only vital points be fortified, and these were considered to be the Royal Dockyards at Portsmouth, Chatham, Plymouth, Portland Harbour, Milford Haven and elsewhere. These forts became known as the Palmerston Forts. Portsmouth harbour, in particular, was given a new encircling line of forts to protect it from landward and seaward attack.

Queen Victoria supported the scheme. Its chief opponent was William Ewart Gladstone, then Chancellor of the Exchequer, who resigned in protest when it was accepted.

By the time the fortifications were completed in the 1880s it was clear that the French had not seriously planned to invade. The Franco-Prussian War of 1870–71 removed the threat and the forts became known as Palmerston's Follies. As a key purpose of fortification is deterrent, this judgement was harsh, but with the rapid development of warship design during the period, the time taken to plan and implement the works would always have caused problems with ensuring that the defences were capable of defeating a French attack force.