This last achievement was the perfecting of a machine to aid in the great World War and you will find the details set down in the volume which immediately precedes this. "Tom Swift and His War Tank," it is called, and in that is related how he not only invented a marvelous machine, but succeeded in keeping its secret from the plotters who tried to take it from him. In this Tom was helped by the inspiration of Mary Nestor, whom he hoped some day to marry, and by Ned Newton, a chum, who, though no inventor himself, could admire one.
Ned and Tom had been chums a long while, but Ned inclined more to financial and office matters than to machinery. At times he had managed affairs for Tom, and helped him finance projects. Ned was now an important bank official, and since the United States had entered the war had had charge of some Red Cross work, as well as Liberty Bond campaigns.
Somehow, as she sat there in the craft which seemed disabled, Mary Nestor could not help thinking of Tom's many activities, in some of which she had shared.
"Oh, if he falls now, and is killed!" she thought. "Oh, what will happen to us?"
"It's all right, Mary! Don't worry! It's all right!" cried Tom, through the speaking tube.
"What's that? I can't hear you very well!" she called back.
"No wonder, with the racket this motor is making," he answered. "Why can't something be done so you can talk in an aeroplane as well as in a balloon? That's an idea! If I could tell you what was the matter now you wouldn't be a bit frightened, for it isn't anything. But, as it is—"
"What are you saying, Tom? I can't hear you!" cried Mary, still much frightened.
"I say it's all right—don't get scared. And don't jump!" Tom shouted until his ears buzzed. "It's all nonsense—having a motor making so much noise one can't talk!" he went on, irritatedly.
A strange idea had come to the young inventor, but there was no time to think of it now. Mentally he registered a vow to take up this idea and work on it as soon as possible. But, just now, the aeroplane needed all his attention.