For a moment Frank could not. Henri's eyes were sharper than his. But then he did make out vaguely two immense shapes that were coming through the air. Soon, too, the faint hum of their powerful motors made itself heard.
"Zeppelins and big fellows, too," said Frank. "All the better!"
He wondered if his plan would work, and if he would be able to carry it out. If, in the final test, would he dare to do what he had tried to arrange? Time enough to think of that when the moment for decision came. And meanwhile there were a hundred things that might happen to ruin his plan. There was nothing to do now but wait. But every moment of waiting brought the climax nearer. The hum of the motors of the airships rose louder on the quiet air, broken only by the faint and distant mutter of the battle that was still being fought miles away. It sounded now like the buzzing of a swarm of bees, magnified a thousand times. And then the field was full of men, rushing from the inn. He wondered how they could have been concealed there. But such wonder was idle, and he did not think of it. Instead he watched keenly. First one monstrous aerial battleship came to rest on the earth. At once the men in the field surrounded her, seizing the ropes that were flung out, and made her fast.
There was a good deal of noise. Men were calling in German of course. But soon order was restored, and the only voices were those giving commands. Suddenly Frank's face lighted up.
"Did you understand, Henri?" he said. "The men in the field are to be the crews for the fighting. They have sailed here with only enough men to steer them. And now all are ordered out, to stretch their legs!"
"Yes, I heard that order," said Henri.
"Now keep your eyes glued to them. What are they doing?"
They listened and watched intently.
"Just as I thought," said Frank. "See, they are going to fill the tanks. There, they are attaching hose. And they have a pump—they surely must have a pump, to send the petrol uphill!"
Meanwhile the other airship had come down, on the other side of the barrels, and there as nearly as they could judge, the same procedure was carried out.