When Lieut. Alan Shields of the Royal Navy maneuvered his black Capri through rush-hour traffic in Belfast last week, he knew he was in a combat zone: the Irish Republican Army had recently stepped up its terrorism, especially against British servicemen in Northern Ireland. What the 45-year-old officer did not know was that his car had been booby-trapped with explosives. As he pulled away from a traffic light, a powerful blast tore through his car, incinerating Shields and the car in a ball of flame.
Less than 72 hours earlier, in Ballygawley, 40 miles west of Belfast, another I.R.A.-triggered explosion blew...