AP Photo

Almost exactly 30 years ago, in the summer of 1979, an IRA double ambush killed 18 British soldiers near the town of Warrenpoint in Northern Ireland. Among them was the commanding officer of the Queens Own Highlanders, Lieutenant-Colonel David Blair. It was the worst single incident during a campaign that lasted nearly two decades and cost more than 700 military lives.

Yet, despite the occasional opinion poll suggesting that the Irish should be left to sort things out for themselves, and a desultory Troops Out campaign waged by the Daily Mirror, there was never any great public movement for withdrawal.

Three years later, though still mired in Ulster, British Forces travelled thousands of miles to liberate some barely populated islands from Argentina, at a cost of 258...