On December 6, 1917, the munitions ship Mont Blanc blew up in Halifax, Nova Scotia. The blast had one-sixth the power of the first atomic bomb and killed or wounded 20 percent of the Halifax population. The enormous ensuing relief effort was a success. Relief workers limited further loss of life, maintained order, and restored Halifax's wartime role as a critical port. Halifax was a military town, and forces from Canada, Great Britain, and the United States played a significant role in the relief effort. This study proposes that military contributions were critical to this successful humanitarian assistance operation. First, it provides a background of Halifax, the explosion, and a brief description of the military units involved. Next, it examines the three most critical military contributions to the relief effort: enough trained men and equipment to provide an immediate emergency response for medical care; authority to enforce security in the ruined town, enabling streamlined relief; and vital leadership to organize a systematic relief effort. Without these contributions, the relief effort would not have proceeded as quickly or successfully. The study concludes with implications for today's humanitarian assistance missions for which military forces are well suited, and the argument that the capability is a critical part of national strategy.