"Yes, I've worked on them, too, but the engineering part is my specialty. I'm a little out of my element on a trip-hammer." "I see. Well, perhaps I'll give you a trial. Meanwhile you might break Koku in on operating this machine. If I transfer you I'll put him on this hammer." "Thank you, Mr. Swift! I'll show him all I know about it. Oh, there goes the hammer again!" he exclaimed, for, as he started it up, as Tom turned away, the big piece of steel once more jammed on the channel-plates. "Me fix!" exclaimed the giant eagerly, anxious for a chance to exhibit his great strength. "Wait a minute!" exclaimed Tom. "I want to get a look at that machine." He inspected it carefully before he signaled for Koku to force the hammer back into place. But, if Tom saw anything suspicious, he said nothing. There was, however, a queer look on his face as he turned aside, and he murmured to himself, as he walked away: "So you want to be transferred to the airship department, do you? Well, we'll see about that. We'll see." Tom had more problems to solve than those of making an aerial warship that would be acceptable to the United States Government. Ned Newton called on his chum that evening. The two talked of many things, gradually veering around to the subject uppermost in Tom's mind--his new aircraft. "You're thinking too much of that." Ned warned him. "You're as bad as the time you went for your first flight." "I suppose I am," admitted Tom. "But the success of the Mars means a whole lot to me. And that's something I nearly forgot. I've got to go out to the shop now. Want to come along, Ned?" "Sure, though I tell you that you're working too hard--burning the electric light at both ends." "This is just something simple," Tom said. "It won't take long." He went out, followed by his chum. "But this isn't the way to the airship shed," objected the young bank clerk, as he noted in which direction Tom was leading him. "I know it isn't," Tom replied. "But I want to look at one of the trip-hammers in the forge shop when none of the men is around. I've been having a little trouble there." "Trouble!" exclaimed his chum. "Has that plot Lieutenant Marbury spoke of developed?" "Not exactly. This is something else," and Tom told of the trouble with the big hammer. "I had an idea," the young inventor said, "that the man at the machine let it get out of order purposely, so I'd change him. I want to see if my suspicions are correct." Tom carefully inspected the hammer by the light of a powerful portable electric lamp Ned held. "Ha! There it is!" Tom suddenly exclaimed. "Something wrong?" Ned inquired.