The third volume of the series, “Navy Boys Behind the Big Guns; Or, Sinking the German U-Boats,” took our heroes into perils and adventures which they will long remember, for they included work in the gun turrets of the _Kennebunk_, a wreck that threatened the lives of all four chums, a mix-up with German spies, and finally a record trip across the Atlantic by which the huge superdreadnaught arrived at the rendezvous in time to take part in a naval engagement which put a part of the Hun navy to flight. Now the four friends were back on the _Colodia_ which was doing patrol duty off the English and French coasts, and convoying troop and food ships through the submarine and mine zones. The base of the squadron of which the destroyer was a member was at this English port, on the hillside above which Philip Morgan, Alfred Torrance, Michael Donahue and Ikey Rosenmeyer have been introduced just as they met the American sailor lad, George Belding, and his doubtful friend, the giant ex-coster, “Willum” Johnson. “Keep cool,” Whistler urged again, as the Zeppelin sailed inland. “There is no use running----” His further speech was smothered by a terrific explosion from the port below. A lurid burst of flame, stronger than the sunlight, shot into the air where a wharf and warehouse had been. Smoke followed, instantly hiding the mark the bomb from the Zeppelin had found. This daylight raid was the boldest the Germans had attempted. The enemy must have supposed the fog was over the land as well as the sea, or he would never have risked the attack. Again a nerve-racking explosion following a flash of light that seared their eyeballs, and the middle of the town--the market place--was shrouded by thick smoke. “The dirty ’ounds!” bawled the British seaman, suddenly finding his voice. “The dirty ’ounds! They’re killin’ women an’ kids down there! Lemme get my bloomin’ ’ands on ’em!” He dropped George Belding’s collar at last and would have started in a clumsy run down the hill. It was Whistler who stopped him, with a two-handed grip on the Englishman’s collar now. “What good would you be down there, man?” the American youth demanded. “You’d only get yours, too, maybe. Those bombs are falling two or three thousand feet.” “Argh!” growled Willum Johnson, shaking his huge fists in the air, his face raised to the coming Zeppelin. The growl was animal-like, not human. “Argh! Lemme get ’em----” A third bomb exploded. A big house below them, half way down the hillside, disappeared. It was as though a monstrous sponge had been wiped across that spot and erased the building! “Oh! Look out! Look out!” sobbed Frenchy, and covered his eyes with his hands. His chum Ikey shook beside him, but could not close his eyes to the horror.