But they had done their work. A hundred torpedoes, driven by their motors of compressed air just below the surface, were steering automatically for the Austrian battleships. Suddenly the fourth ship of the Austrian line staggered; a white spray of water leaped high in the air, and the Austrian vessel split into many pieces. The first torpedo had gone home. The fifth and sixth Austrian battleships also now leaped from the water, and then sank from sight. Farther back another Austrian ship dropped from the line of battle. Now a school of Austrian torpedo craft dashed forward again. They were met by a fierce hail of fire from the French, but in spite of this they succeeded in launching their torpedoes, and the French battleship, far back, suddenly disappeared from the surface of the Adriatic. Now the battle grew so terrific that individual ship movements could not be kept track of. The Austrian torpedo craft retreated and the French gave chase. Jack and Frank saw all this, soaring above the sea, a part of it, and yet not a part of it, for so far they had had little to do. Pierre, seated in front of Jack, suddenly uttered a shout. Following the direction of the pilot's eyes, Jack perceived a great, gray, pencil-shaped object approaching through the air. He recognized it instantly--a German war dirigible, sent to help the Austrians. Under it flew smaller forms, aeroplanes accompanying it as guard. And now a second Zeppelin appeared--and then a third. Swiftly they swept over the sea. A moment and they had passed over the broken line of Austrian battleships, and sped on toward the French fleet. The French perceived the menace, and their special quick-firers, elevated for aeroplane defense, came into action. But the Zeppelins bored on, and their powerful guns fired down macarite shells. The first French battleship, already stripped by the raking fire of the Austrian fleet, seemed to crumple up, and a moment later disappeared altogether. The rain of shells from above found breaches in the armor of a second French ship, caught a magazine forward and exploded it, almost at the same time blew up a magazine aft, and the ship, broken in two, sank. The first dirigible, having passed over the French fleet, now turned and came back. The shells of the ships burst harmlessly below it. As the torpedo boats had gathered for an attack against the Austrian fleet, so now did the French aircraft gather for an assault upon these enemies of the air. But the enemy's airmen did not wait for them. They charged. Machines met, wing against wing, and toppled into the water. Others, their propellers crushed, met the same fate. But some of the French machines burst through, only to be met by the deadly fire of the Zeppelins and sent into the sea.