The order was instantly obeyed by the whole division, and the fifty battleships simultaneously sank out of sight to engage the invisible enemy, while the Sultan and his companions on board the air-ships waited in intense anxiety to see what the next few fateful minutes would bring forth. No human eye could see what work of death might be going on down in the depths of the sea. Even those who took part in it would know it only by its results, and of these only the victors would know anything. They would reappear on the surface of the waves, but the vanquished would never rise again. Minute after minute passed and still the anxious watchers on the air-ships saw nothing. The bright, sunlit waves rippled on over the abyss in which the conflict must by this time be almost over. Five, ten, fifteen minutes passed, and still no sign. Had Khalid been a mile or two farther on and closer down to the surface of the sea, he would have seen streams of air-bubbles rising swiftly here and there and instantly breaking. But from where he was he could see nothing. Five more minutes went by and suspense gave place to apprehension. Had the whole of the first division simply sunk to its destruction into some invisible trap that had been laid for it deep down in the watery abyss? If not, how came it that not even one of the battleships had risen to the surface to tell the tale of victory or defeat? Khalid knew that the squadron would obey orders and hurl itself at full speed, that is to say, at some hundred and fifty miles an hour, upon the enemy the moment the tell-tales found their mark. In two or three minutes--five at the outside--their rams must either have done their work or failed to do it. If they had done it they would have risen to the surface; if they had failed and themselves escaped destruction they would still have risen. Now twenty minutes had passed and not one of the fifty battleships had reappeared. What could this mean but disaster? And disaster it did mean, but great as it was it was as nothing compared with the frightful catastrophe which followed close upon it. All eyes on board the air-ships were so intently fixed upon that portion of the sea where the squadron was expected to rise again that no one thought for the moment of looking back towards the transports until the dull rumbling roar of a series of explosions came rolling up out of the distance. Instantly every glass was turned in the direction whence the sound came, and Khalid saw his great fleet of troopships tossing about in the midst of a wild commotion of the waves, out of which vast masses of white water spouted as if from the depths of the sea, and amidst these ship after ship heeled over and sank into the white seething waters.