Royal Commission on the Defence of the United Kingdom

The appointment of the Commission had been prompted by public concern about the growing military and naval power of the French Empire and was instigated by the Prime Minister, Henry Temple, 3rd Viscount Palmerston, who came to be closely associated with the project.

Many of the recommendations were acted upon; however, the great expense, the length of time taken to complete the various works and their perceived usefulness were all subjects of critical political, press and public debate.

[1] When Palmerston returned to power in 1859, public concern over this naval arms race, combined with Napoleon III's aggressive intervention in the Second Italian War of Independence, allowed him to act on his conviction that Britain's coastal defences were inadequate to prevent invasion if the Royal Navy was lured elsewhere.

Armstrong's opinion was that his latest guns would be able to defeat some features of current fortification, such as the Carnot wall, but that the maximum range of artillery would be unlikely to exceed 5 miles (8.0 kilometres) in the future.

Further, that the coastline which they considered to be at risk, the 700 miles (1,100 km) from the Humber to Penzance, could not feasibly be completely fortified and therefore recommended that "the fortifications of this country should be confined to those points... whose possession would give him sure bases for operations".

[13] The government, although broadly in agreement with the report, thought that it was too ambitious to be accepted by Parliament in its original form, and therefore set about reducing the number of planned works while attempting to retain the objectives of the scheme for each locality.

Planned forts that were not proceeded with included fifteen at Plymouth, ten at Pembroke, six at Portsmouth and four at Chatham; the floating batteries were also dispensed with, resulting in a total saving of £3,930,000.

The chief opponents were the Radical Richard Cobden and his ally, William Ewart Gladstone, then Chancellor of the Exchequer, who between them had recently concluded the Cobden–Chevalier Treaty, a Free Trade agreement with France.

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.

[16] The landward fortifications were intended to prevent an enemy force who may have landed at an undefended beach from marching overland and assaulting a dockyard from the rear, or simply bombarding it.

Construction of some landward forts at Portsmouth and Plymouth had already begun in the 1850s and work on the ring fortress at Chatham was not started until 1875, resulting in very different designs as military theories changed over the decades.