Two more shells, one immediately after the other, now landed on the stern. Clouds of black smoke began to rise, and below tongues of flame presently appeared, licking their way in the direction of a large quantity of ammunition, cordite, and other high explosives. It was not decoy smoke and decoy flame this time. Captain Campbell, watching the whole proceeding from the bridge, perhaps felt something in the nature of a chill creeping up his spine when he realized that the after-part of the ship, where men, explosives, and guns lay concealed in close proximity, was on fire. Just at this moment he observed that the submarine was rapidly approaching; and in a few minutes it lay within 400 yards of his guns. Captain Campbell was just about to give the orders to open fire when the wind took up the dense smoke of the fire and wafted it between his ship and the submarine. This precipitated one of the crises which tested to the utmost the discipline of the mystery ship. The captain had two alternatives: he could fire at the submarine through the smoke, taking his chances of hitting an unseen and moving target, or he could wait until the enemy passed around the ship and came up on the other side, where there would be no smoke to interfere with his view. It was the part of wisdom to choose the latter course; but under existing conditions such a decision involved not only great nerve, but absolute confidence in his men. For all this time the fire at the stern was increasing in fierceness; in a brief period, Captain Campbell knew, a mass of ammunition and depth charges would explode, probably killing or frightfully wounding every one of the men who were stationed there. If he should wait until the U-boat made the tour of the ship and reached the side that was free of smoke the chances were that this explosion would take place before a gun could be fired. On the other hand, if he should fire through the smoke, there was little likelihood of hitting the submarine.