...the 1917 Halifax Explosion—the largest man-made blast of the preatomic age. On the morning of Dec. 6, 1917, the SS Mont-Blanc entered Halifax’s harbor carrying thousands of tons of explosives en route from New York to France for use in World War I. The Norwegian steamship SS Imo, traveling above the speed limit and in the wrong lane, was exiting the harbor. They collided. Unaware of the Mont-Blanc’s cargo, crowds gathered to see the fire. A sailor appraised train dispatcher Vince Coleman of the danger, and rather than flee, Coleman warned incoming trains: “Hold up the train. Ammunition ship afire...