Seventy years ago, the British Empire claimed its last piece of territory – a bleak and uninhabited island, 260 miles (420km) west of Scotland's Outer Hebrides. In 1955, a Royal Navy commander told the BBC about securing Rockall, which remains the site of rival claims even today.

In 1956, the British naturalist James Fisher described Rockall as "the most isolated small rock in the oceans of the world" – and understandably so. The island of Rockall is almost unimaginably remote, an 11-hour boat ride from Scotland's Outer Hebrides, and it is also tiny, measuring a mere 82ft (25m) wide, with a summit only 56ft (17m) above sea level. Most of it consists of bare, near-vertical granite, with just one small patch measuring 11ft by 4ft (3.5m by 1.3m) which is level enough to stand on. As insignificant as this jagged stone outcrop might appear, though, Queen Elizabeth II authorised the annexation of Rockall on 14 September 1955, instructing the Royal Navy to "take possession of the island on our behalf".

Rockall's exact position was first charted by Royal Navy surveyor Captain ATE Vidal in 1831, but it was not until 1949 that Rockall became more widely known, after its name was given to one of the sea areas on BBC Radio's Shipping Forecast. It was around this time that the UK government recognised Rockall's strategic significance. As the Cold War intensified and Nato and Soviet submarines regularly patrolled the North Atlantic, securing Rockall was viewed as key to controlling sea space. Moreover, 230 miles (370km) east, on South Uist in the Outer Hebrides, the UK had established its first test site for US-made guided nuclear missiles. Nato documents, declassified in 1970, revealed the government's fear that "hostile agents" would install themselves on Rockall to spy on the results of the tests.

A Royal Navy survey ship, HMS Vidal, reached the rock on 15 September 1955, but it would be another three days before high winds subsided enough to allow a helicopter to winch three Royal Marines on to it, along with James Fisher, a civilian scientist. There, the men planted the Union flag and formally claimed the islet for Britain. "I had an instruction from Her Majesty to annexe the island of Rockall in her name," Commander Richard Connell, captain of HMS Vidal, told the BBC reporter Neville Barker shortly after the landing. "We sent a signal to the Admiralty saying, 'Operation Rockall successfully completed.' I was never so glad to send any signal in my life."

Fisher was tasked with taking rock samples from the islet for study by the British Geological Society. Rockall was formed from the remains of an eroded volcano, and the granite found there was "apparently unique", Fisher told the BBC. Years later, geologists studying Rockall granite would identify a new........

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