Soon, from raw recruits the boys had been developed into skillful soldiers, as is shown in the second volume of the series, entitled: "Army Boys in the French Trenches; Or, Hand to Hand Fights with the Enemy." The Spring of 1918 had now arrived, and the Germans were preparing for the last desperate drive, on the success of which their fortunes depended. If they could once break through the Allied lines and seize Paris or the Channel ports they would have come near to winning the war, or at any rate, would have greatly delayed the Allies' final victory. The Americans were brought to the front to check the thrust of the Crown Prince's army toward Paris, and the old Thirty-seventh found itself in the very van of the fighting. Tom was captured, and had a series of thrilling experiences before he was able to escape and rejoin his comrades. Nick Rabig came out in his true colors, and his guilt as a traitor was discovered by Tom, while hiding in the woods. How the boys were brought again and again within arm's length of death in the terrific fighting is told in the third volume of the series, entitled: "Army Boys On the Firing Line; Or, Holding Back the German Drive." On July eighteenth, Marshal Foch struck like a thunderbolt and hurled the foe back in a headlong retreat. Again and again the Germans tried to rally, but the Allies were fired with the certainty of victory and would not be denied. Frank and his comrades were wherever the fighting was thickest, and did their full share in driving the Germans back to the Rhine. An event which for a time put Frank under a cloud, because it looked as though he were involved in the robbery of a paymaster's clerk, ended in showing that Nick Rabig was the real culprit. This completely vindicated Frank, as will be seen in the fourth volume of the series entitled: "Army Boys In the Big Drive; Or, Smashing Forward to Victory." That victory was now in sight. The German cause was doomed. One great victory remained to be gained, the clearing of the Argonne forest, wild, tangled, meshed with thousands of miles of barbed wire, crowded with machine gun nests and swept with a hurricane of shot and shell. But nothing could stop America's boys now that their blood was up, and they did much in helping to win here the final and greatest battle of the war. All the Army Boys, fighting like tigers, came through unharmed, except Bart, who was wounded and afterward wandered away from the hospital while temporarily insane.