To say that this sudden and unexpected catastrophe spread panic through the Moslem capital would be but a very inadequate description of the _Avenger’s_ first blow in the world-war. Consternation, wild and unbounded, blanched every cheek, and made every heart stand still as the mighty roar of the explosion burst upon the deafened ears of the inhabitants and then instantly died into silence, broken only by the crash of falling ruins and the screams and groans of the wounded and dying. The red spectre of war in its most frightful form had suddenly appeared to the terrified and horror-stricken vision of millions of men and women, scarce one of whom had ever seen a deed of violence done. Khalid, like a wise leader, did all he could to prevent the panic spreading to the troops on board the transports by issuing peremptory orders for the expedition to start at once. At the same time he signalled for half a dozen air-ships to ascend as far as possible and attempt to discover the source from which the inexplicable attack had come, an errand destined to be entirely fruitless. In orderly succession the hundred huge transports, each carrying from eight to ten thousand men, left the outer basin in two long lines in the rear of the fifty air-ships already in position. A hundred submarine battleships took up their stations five hundred yards in advance of the first line of transports. Fifty of these sank to a depth of thirty feet, and shot two thousand yards ahead as soon as the whole flotilla was in motion, while the other fifty ran along the surface of the water with their conning-towers just showing above the waves, ready to sink in obedience to any signal that their commanders might receive from the air-ships, which commanded an immense range of vision over the waters. To all appearance the enemy was content with the one terrible blow that had already been struck. The smooth, sunlit sea betrayed no trace of a hostile vessel, and as far as the glasses of those on board the air-ships could sweep the sky nothing but the blue atmosphere, flecked here and there with white, fleecy clouds, could be seen. But the Moslem commanders were far from being deceived by these peaceful appearances. From Sultan Khalid, who was commanding the expedition in person, to the engineers who worked the transports, all knew that the invisible line of the Federation patrols had to be passed somewhere in the depths of the sea before the shores of Italy could be reached.