It has been frequently suggested to me that I write of my experiences at the front. As one of the advance-guard of the American army who participated in the great struggle for freedom long before the United States espoused the cause of the Allies, I am more than willing to do this, owing to my strong desire that the public should know something of the constant fighting which is going on _underneath_ as well as on the surface and above the ground of the trenches both in France and elsewhere, especially if, by so doing, I can help the people at large more fully to appreciate the importance of the work and the unflinching devotion of that branch of the army which but seldom finds itself singled out for the bestowal of special honors or for the expression of public approbation. This narrative will be mainly concerned with the engineers and sappers who are so quietly and unostentatiously undergoing extraordinary hardships and dangers in their hazardous work below the ground, in order that their comrades of the infantry may occupy them above, safe, at any rate, from underground attack. In no species of land warfare is a cool head and clear brain, combined with decisive and energetic action and determined courage, more required than in the conduct of these military mining operations. The value of mines and of similar contrivances of the engineer is partly psychological. Though hundreds of men only may be put out of action by their use, thousands of valuable fighting men suffer mentally from the knowledge or from the mere suspicion that their trenches are undermined by the enemy. Such a suspicion causes the strain on their morale to be very severe and their usefulness to be correspondingly diminished.