The air-forts! And it was between them, between their two mighty lines, that the First Air Chief had purposely led the European fleet, I saw now. For _this_, then, was the new device of the air-forts of which he had spoken to us before our start, this device which enabled them to surround themselves with a great cloud-bank that kept them hidden from all and unsuspected by any enemy. Some device for projecting forth great masses of water-vapor it must be, that had enabled them to form that great artificial cloud-bank about themselves. And when the First Air Chief, staking all upon the device, had led the pursuing European fleet into that great cloud-bank, into that giant ambush of the air-forts, then with our own fleet dropping down out of it they had needed only to disperse the artificial cloud-mass about them by means of great air-jets of terrific power, to disperse the cloud-mass and to turn all the fury of their great guns upon the European fleet that hung still dazed there in the withering fire of those suddenly-unmasked batteries! For now above us the European ships, whirling aimlessly about in that terrific fire that raked them from either side, were falling faster still! Their own shells burst and flared along the sides of the great air-forts, but were too few in number to cripple or destroy any of those gigantic, heavily-armored edifices. And at that moment, even as the European ships strove to mass together to escape from that great death trap of the air, the First Air Chief's ship was slanting up toward them, and now we needed no orders to follow as we raced up after him. Up until our great fleet rushing upward in a single mass was pouring up before us a third terrific fire of heat-shells which, added to that of the air-forts on either side, sent blinding death-flares dancing and leaping over all the mass of ships above us. [Illustration: And now above us the European ships, whirling about aimlessly in the terrific fire that raked them from either side, were falling faster still. And even as they massed together to escape that great death trap, we were slanting up after them.] "They're turning!" cried Hilliard. "They're fleeing!" Homeward