The officers of the American mining regiment were engineers who had had practical experience in all those far-off regions where men seek their fortunes in the earth. One of them, a young lieutenant, was diamond-mining in the Katanga district of the Congo when word reached him by native runner that the United States had decided to take a hand in the Great War. It took him four months of uninterrupted travel by horse, wagon, rail, and boat to reach the United States and offer his services to the Chief of Engineers. Another of our mining officers was a prisoner of the revolutionists in Mexico when the rumor penetrated to his prison cell that the United States had gone to war. That night he overpowered his guards, scaled the prison wall, made his way on foot across northern Mexico, the journey being relieved from monotony by several hairbreadth escapes from bandit bands, and reached the border in time to join the Engineers and go to France with one of the first contingents. In former wars military mining was almost wholly confined to siege operations; that is, driving galleries under fortified positions and blowing them up. But the Great War developed an entirely new system of mining tactics, which included frontal and flank attacks, raids, enveloping movements, and other phases of war as fought on the surface of the earth. “Unlike the soldier who fights above ground,” explained a mining officer, “the miner has to be prepared for attacks not only against his front and flanks, but for assaults which may come from overhead or from underneath. In other words, he has four flanks to defend instead of two.”