The Archdale story begins in 1614, when John Archdale arrived from Norfolk as one of the English undertakers of the Plantation of Ulster, the Jacobean scheme that handed confiscated Maguire lands to settlers loyal to the Crown. By 1615 he had thrown up a T-plan tower house surrounded by a defensive bawn sixty-six feet by sixty-four, fifteen feet high, with stone flankers projecting at each corner so musket fire could rake the walls. It was a fortress built for a frontier the planters never fully tamed. In 1641 the Irish rose, and Rory Maguire burned the castle to the ground in the rebellion that scorched its way across Ulster. The Archdales rebuilt. In 1689, in the upheavals of the Williamite war, the castle was destroyed a second time. The original ruin still squats in the old corner of the park, its broken stones a quieter monument than the cobbled courtyard up the slope.

In 1773 the family abandoned military architecture and built a proper Georgian mansion roughly a mile southwest of the old castle, the kind of pillared, symmetrical pile that announced a Protestant Ascendancy family had arrived. For over a century and a half it sat above the lough as a gentleman's seat. Then came 1939, and the Air Ministry came knocking. The manor was requisitioned as the wartime headquarters for RAF Castle Archdale, its drawing rooms repurposed for briefing maps and weather charts. After the war the house fell out of use, neglected by an emptying estate, and in 1970 the demolition men finally came. What remains is the huge cobbled courtyard, ringed by white outbuildings that now hold an information centre and tearooms, and the absence at the centre where a great house used to be.

RAF Castle Archdale housed up to 2,500 personnel at its wartime peak, making it briefly one of the largest places of habitation in Fermanagh. The problem was geography. The lough drained west into the Atlantic, but to reach the convoy lanes a flying boat had to skirt north around the neutral Republic, an exhausting detour that ate into patrol range. So the Irish Taoiseach Eamon de Valera, neutral on paper but quietly pragmatic, gave permission for a narrow strip of Donegal airspace to be used. Sunderlands and Catalinas from Castle Archdale flew the so-called Donegal Corridor from Belleek in Northern Ireland over Ballyshannon in the Republic and out into open sea, gaining hours of fuel and hundreds of miles of cover. The arrangement was never publicly acknowledged during the war. It almost certainly saved Allied lives in the North Atlantic.

On 26 May 1941, the Bismarck was alone, wounded, and running for the safety of occupied France. The Home Fleet had lost her in heavy weather thirty-one hours earlier. Two Catalinas lifted from Castle Archdale and pushed west into the Atlantic murk. At ten thirty in the morning, one of them broke through cloud and saw the unmistakable silhouette below: a single capital ship, course south-southeast, doing what looked like twenty knots. The sighting report flashed back through the corridor, and within hours Swordfish from HMS Ark Royal were boring in with torpedoes. One of them jammed the Bismarck's rudder twelve degrees to port, locking her into a slow circle. The next morning Home Fleet battleships closed and finished her. The crews who flew from this Fermanagh marina were, in a literal sense, the eyes that decided the chase.

Today Castle Archdale Country Park is run by the Northern Ireland Environment Agency. Walking trails thread through mixed woodland that hides badger setts and red squirrel dreys. A small museum holds wartime exhibits, including photographs of moored flying boats and the strained faces of crews who flew sixteen-hour patrols. From the marina, a ferry crosses to White Island, where seven stone figures of uncertain age, half pagan and half Christian, stand built into a ruined church wall. The caravan park itself sits on the very concrete that once cradled Catalinas. A private railway station served the estate from 1866 to 1950. Almost nothing here is what it first seems.