That was the point. It might be interesting to the German staff to know the locations of British troops in England, and, more especially, their destinations if they were going abroad as part of an expeditionary force to France or Belgium. But the information would not be vital; it didn’t seem to Harry that it was worth all the risk implied. But if, on the other hand, there was some plan for a German invasion of England, then he would have no difficulty in understanding it. Then knowledge of where to strike, of what points were guarded and what were not, would be invaluable. "But what a juggins I am!" he said. "They can’t invade England, even if they could spare the troops. Not while the British fleet controls the sea. They’d have to fly over." And in that half laughing expression he got the clue he was looking for. Fly over! Why not? Flight was no longer a theory, a possibility of the future. It was something definite, that had arrived. Even as he thought of the possibility he looked up and saw, not more than a mile away, two monoplanes of a well-known English army type flying low. "I never thought of that!" he said to himself. And now that the idea had come to him, he began to work out all sorts of possibilities. He thought of a hundred different things that might happen. He could see, all at once, the usefulness Bray Park might have. Why, the place was like a volcano! It might erupt at any minute, spreading ruin and destruction in all directions. It was a hostile fortress, set down in the midst of a country that, even though it was at war, could not believe that war might come home to it. He visualized, as the truck kept on its plodding way, the manner in which warfare might be directed from a center like Bray Park. Thence aeroplanes, skillfully fashioned to represent the British ’planes, and so escape quick detection, might set forth. They could carry a man or two, elude guards who thought the air lanes safe, and drop bombs here, there–everywhere and anywhere. Perhaps some such aerial raid was responsible for the explosion that had freed him only a very few hours before. Warfare in England, carried on thus by a few men, would be none the less deadly because it would not involve fighting. There would be no pitched battles, that much he knew. Instead, there would be swift, stabbing raids. Water works, gas works, would be blown up. Attempts would be made to drop bombs in barracks, perhaps. Certainly every effort would be made to destroy the great warehouses in which food was stored. It was new, this sort of warfare; it defied the imagination. And yet it was the warfare that, once he thought of it, it seemed certain that the Germans would wage.