It was lunchtime on April 18, 1983, and the cafeteria of the American Embassy in Beirut was buzzing with customers. At about 1 p.m., a powerful blast tore apart the front of the seven-story building. The bomb, hidden in a van reportedly stolen from the embassy 10 months earlier, killed 63 employees, including 17 Americans.

It was the first time that a U.S. embassy had become a terrorist target, and it forever changed the way the Diplomatic Security Service (DSS), the State Department’s law-enforcement division, operates around the world.

“The bombings of the embassy in West Beirut in 1983 and of the embassy annex in East Beirut in 1984 were a major catalyst for creating the Bureau of Diplomatic Security,” which oversees the DSS, said John C. Murphy, special agent in charge of Secretary of State Colin L. Powell’s protective detail and a DSS agent for 29 years…