was required, under ordinary conditions, of the infantrymen. They were expected to possess a fluent knowledge of German and to be able to both speak and understand it as well as they did English, though this requirement was not always fulfilled toward the end. They were thoroughly coached, moreover, in German military phrases and colloquialisms and had to be proficient in recording ground-telegraphy code, which, though slow, is extremely difficult to master. It will be seen, therefore, that the Listening-In Service demanded of its operators continuous interest and constant vigilance, together with a sufficiently active imagination to enable them to piece together the broken or garbled fragments of messages which their instruments might pick up, and to deduce from these messages what the enemy was doing or what he intended to do. Listening-in was very far from being a one-sided game, however, for the Germans, who were thoroughly conversant with its possibilities and limitations, maintained a service which was nearly, if not fully, equal to our own. The real superiority of our service lay, not in its equipment, but in the boyish enthusiasm of its personnel, many of whom were university undergraduates when the war began. With them the work never assumed the aspect of a daily task which had to be performed whether they liked it or not: they regarded it rather as a game, interesting, fascinating, exciting. The quickness with which they grasped the technicalities of the service was amazing. I knew of one case where a soldier of a Listening-In Section, wholly without previous experience in the work, overhearing a telephone conversation in the enemy’s lines which indicated that the watches in that sector were being synchronized, deduced that a raid on the American trenches was being planned. He promptly acquainted the divisional intelligence officer with his conclusions, and when the Germans launched their attack, expecting to take the _verdamte_ Yankees completely by surprise, they were greeted by a burst of rifle and machine-gun fire which almost annihilated them. After the moving warfare began it was, of course, extremely difficult to maintain these listening-stations, but when the advance halted, even for a night, listening-stations were always established if conditions permitted.