Crownhill Fort is a Royal Commission Fort built in the 1860s in Crownhill as part of Lord Palmerston's ring of land defences for Plymouth. Restored by the Landmark Trust, it is now home to several small businesses, museums, exhibitions and a holiday apartment sleeping up to eight people. The Fort is open to the public on the last Friday of each month and hosts tours for local schools and societies at other times.

The Royal Commission on the Defence of the United Kingdom was a committee formed in 1859 to enquire into the ability of the United Kingdom to defend itself against an attempted invasion by a foreign power, and to advise the British Government on the remedial action required. 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. In the following year, the Commission's report recommended a huge programme of fortification to defend the country's arsenals and naval bases. 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.