"The objective point is Mannheim on the Rhine. The river is eighty miles due east, and Mannheim is about fifty miles farther down the river. That city is on the eastern bank of the river, and Ludwigshafen is a small town, on the opposite shore where the great laboratory of Badische Analin and Soda Fabrik is located," remarked the lieutenant. "So we are going to destroy a soda factory?" said Ralph with a grin. "Not exactly," replied the lieutenant, amused at the intimation. "The principal thing turned out at the plant before the war was nitrate, a chemical most essential in the manufacture of explosives, and the importance of the place may be understood when I tell you that fully two-thirds of this product used by the Germans comes from that place." "When will the start be made?" asked Ralph excitedly. "Tomorrow," was the reply. "Then I want to see the map," said Ralph. "By all means," answered the lieutenant. "Now, you will notice that here is a canal shown on the map which runs due east. That is the Rhine-Marne, which parallels this river, the Zorn. The Zorn flows into the Rhine at Strassburg. You know, of course, that rivers, or canals, are the best guides for our purposes, so we must get these firmly fixed in our minds." "Yes, that and the towns are sure to carry us along without mistake," remarked Alfred. "What is that place, Saarburg? It is on the river." "That is an ancient town, and you can hardly fail to recognize the place, for it is surrounded by a great stone wall. It also contains a strong garrison. Now note the next important place, twenty miles farther on; that is Zabern. From that place we can see the Rhine at various places, as we intend to fly at an altitude of two thousand meters, or, as you would say, 6500 feet." "Why is it necessary to go to such a high altitude?" asked Alfred. "Because at Saarburg, Zabern and Brumath they have long range anti-airship guns, and we cannot take any chances," replied the lieutenant. The camp was a seething place of excitement the following morning. Twelve of the machines carried bombs exclusively; some of the airplanes had six bombs, each weighing 180 pounds; one had three bombs of 300 pounds each, and the Seraph carried ten 120-lb. high-explosive cylinders. These were placed in a suitable case having compartments, the lower ends of the compartments being provided with outwardly opening doors, capable of being released by the pressure of the foot operating against a lever. "I am going to rig up the cameras so we can take pictures of the explosions," said Alfred, as they made their way to the hangar. "That is a splendid idea," remarked the lieutenant. "Such an enterprise would be commended by the Intelligence Department of the War Office. By all means make the arrangements, for we expect to start in an hour."