Look at a map of NATO's North Atlantic strategy during the Cold War and the answer becomes obvious. Machrihanish sat on the Greenland-Iceland-UK gap, the choke point through which Soviet submarines would have to pass to reach the open Atlantic. From here, anti-submarine aircraft could patrol the approaches to the North Channel. Fighter-bombers could be dispersed forward from English bases. And, more privately, nuclear weapons could be stored at the edge of Europe, ready to fly east if the long-feared war began. The Admiralty turned the existing airfield over to the Air Ministry in May 1963, and the RAF made it available to the US Navy soon after. Between 1990 and 1995 alone, NATO and the Ministry of Defence spent more than £55 million on building works. None of this was secret in any meaningful way, but most of it was unadvertised.

The most distinctive Cold War tenants at Machrihanish were the US Navy SEALs of Naval Special Warfare Group 2. They had a complex of low buildings on the southwest side of the airfield - offices, an armoury, a parachute drying tower, a 25-metre indoor firing range, and a hangar designed so that a C-130 could taxi up and disgorge vehicles directly into the building. A US Marine Corps detachment arrived in 1974 to provide nuclear weapons security; before then, sailors had been guarding the warheads. Special operations rehearsals ran in the Atlantic surf off the Mull. Local farmers occasionally saw black inflatable boats appearing at unlikely beaches. When the Cold War ended, the SEALs went home. The US Navy returned the site to the Ministry of Defence on 30 June 1995, and the buildings sat empty.

From the early 1990s, Machrihanish acquired a small reputation in aviation enthusiast circles for a different reason. Witnesses claimed to have heard unusual aircraft noises overhead and to have seen contrails behaving strangely. The rumours coalesced into a name - Aurora, an alleged hypersonic American reconnaissance aircraft that succeeded the SR-71. The story went that Machrihanish, with its enormous runway and remote location, was an ideal forward operating base for whatever exotic technology the US wanted to keep out of sight. In January 1995 Llew Smith, MP for Blaenau Gwent, put the question to Parliament. The Minister of State for the Armed Forces, Nicholas Soames, denied that any US prototype aircraft was operating from Machrihanish. The Aurora has never been officially acknowledged to exist. The rumours have never quite gone away. Most aviation historians regard the Machrihanish-Aurora story as folklore, but folklore is what people make when a place produces unexplained noises in the sky.

After 1995 the airfield sat under what the MOD called "care and maintenance" - kept usable, mowed, secured, but largely empty. In March 1996 Highlands and Islands Airports Ltd took out a license to operate a portion of the field as Campbeltown Airport, with Loganair flights to Glasgow. The rest of the base waited. In 2008 the MOD finally declared the property surplus and put it up for sale. The local community, organised as the Machrihanish Airbase Community Company, wanted to buy it. The Scottish Government initially rejected their first ballot in 2010 over concerns about the viability of the proposal. They tried again. On 11 May 2012 MACC bought the entire site from the Ministry of Defence for one pound. Around eight hundred local people own it now, each shareholding worth a single share of decision-making about what an Atlantic-facing forward operating base becomes when the war it was built for never comes.

Today the airfield is split between two functions. Campbeltown Airport (EGEC) handles Loganair's twice-daily Glasgow service from a small terminal that opened in the 1990s. The rest of the site is a business park managed by MACC, with the former SEAL buildings repurposed for whatever tenant will take them - whisky storage, light manufacturing, training centres. The runway remains. On clear days private pilots fly in for the experience of touching down on what may be the longest runway you can use without a transponder reservation. The Mull of Kintyre lies south, the Antrim coast east across the channel, the long beach at Machrihanish stretches north along the Atlantic shore. Paul McCartney's farm is a few miles away. The station motto, in Scottish Gaelic, was Airm a dhionadh na fairgeachan - arms to defend the sea. The arms are gone. The sea is still there.