"It has limitations. But it is not useless. Battle conditions may be developed to take the limitations as they may exist. Look. The course of the target is determined--or wait, we must determine the course of the target first. The course of the target is found by lying in wait with detectors. The ship is concealed in the barrier-screen, and the target can not see or detect the sub-cruiser, but the detectors catch the target. The sub-cruiser must remain in the shell, so to speak, until the target is out of detection range. This gives plenty of time to plot the course of the target. Once out of range, the shell is opened and the sub-cruiser takes off on a tangent course at high acceleration. It exceeds the speed of the target, and then turns to intercept the course of the target at some distant spot--calculated on the proposition of the sub-cruiser driving powerless, or coasting. The shell is re-established, and the target and the sub-cruiser converge. At point-blank range, the sub-cruiser lets fly with interferers and torpedoes, and continues on and on until it is out of range once more. "The target is either demolished; or missed, requiring a second try. At worst, the target knows that from out of the uninhabited sky there has come a horde of interferers and torpedoes, and there is nothing to shoot at. They still do not know which way the blast will come from next. Follow?" "Sounds cumbersome," said Greggor. "But it may work." "Is that what you've been working on?" asked Laura. "Yes," said Guy. "Sounds as though we have genius in our midst," she answered, flashing Guy a glance that made his heart leap. "Oh, I--" started Guy, and then remembered the whole tale again. He couldn't really take credit for this. It wasn't truly his idea; that had come from Ertene. The application of the light-shield had been his, but they were giving him credit for the whole thing. That was not fair--and yet he knew that he must take false credit or betray not only himself but Ertene, too. And now that his die was cast, he must never waver from that plan. To do so would bring the wrath of the Board of Investigation for his not telling all upon his arrival. So he stopped the deprecatory sentence and merely smiled. "--don't think it is too wonderful. It is, or was, but a matter of time before someone else struck the same idea." "But you were first!" said Laura. "And we're going to celebrate. Mind if I run off with him?" she asked her parents. She drew him from the dining room without waiting for an answer. VII. From Sahara Base to New York is a solid, two-hour flight for the hardiest driver. Maynard was no tyro at the wheel of a sky-driver, and he drove like fury and made it in slightly over the two-hour mark. He let the flier down in New Jersey and they took the interurban tube to the heart of Manhattan.