"If we stay here long enough, I'll see if I can't get permission to go back and find out," mused Jimmy, as he frantically scraped the earth into a sort of long mound in front of his head. They were under a hot fire now. The American advance had been momentarily checked. And while there is this period in the fighting may I not take advantage of it to make my new readers acquainted with the main characters of this story, and also tell something of the previous books in this series? The initial volume is called "The Khaki Boys at Camp Sterling," and in the pages of that you meet, for the first time, Jimmy, Roger, Bob and Iggy. To introduce them more formally I will say that Jimmy's correct name was James Sumner Blaise, and that he was the son of wealthy parents. He was about nineteen years old, and this was the average age of his comrades. Roger Barlow was an orphan, and had been working in a munition factory when he decided to enlist. Robert Dalton had been a "cub" reporter on a newspaper, and, like Roger, was an orphan. Though Ignace was no orphan, possessing both father and mother and a number of sisters and brothers, his home life was not happy, and he was really glad to join the army. These four lads soon became "bunkies" at Camp Sterling, where they had their training. Later they took into their friendship one Franz Schnitzel, who, though possessed of a German name, was, nevertheless, a loyal "United Stateser," as Iggy called it. Franz had a hard time, at first, convincing people of his loyalty, and once he was accused of a black crime, but later he was proved innocent. After having been trained at the camp, and cementing their friendship in many ways, the "five Brothers" as they called themselves, were sent across. In the second book of the series, "The Khaki Boys On the Way," we find our youthful heroes sailing for France after a series of adventures, one a startling one, at Camp Marvin. This adventure had to do with the blowing up of a bridge, and Jimmy Blaise had a fight with a spy--a fight that came near being Jimmy's last. In this second book will also be found an account of the trip of the Khaki Boys to the coast, where they boarded a transport for France. If they expected to get across safely, as many thousands did, they were disappointed, for they were attacked by a U-Boat. Many on board the transport _Columbia_ perished, but the five Brothers were saved, and, after a time spent in a rest camp in England, they crossed the channel to France. The third volume, called "The Khaki Boys at the Front," tells in detail some of their exciting experiences. The quintette were given leave to go from their camp to Paris, and in that beautiful city they met some other friends, the Twinkle Twins, otherwise John and Gerald Twinkleton, who had joined the aviation branch of the service. This was natural, since their cousin, Emile Voissard, was one of the most daring of the airmen, meriting the name "Flying Terror of France."