Jordan nodded. He felt a little honored that the chief was giving him this explanation in person rather than just turning him over to one of the scientific personnel for a briefing. He did not understand that the old man was troubled and was talking the situation through as much for his own sake as for anyone else's. * * * * * "That's the problem," the chief continued. "Essentially an indestructible machine with a built-in source of power that one can't reach. It had to be built that way--a war instrument, you know." He stopped and looked squarely at the bright young man sitting across the desk. "This lousy war. You'd think the human race would grow up some time, wouldn't you?" He filled a pipe with imported Earth tobacco and lit it, and took a few deep puffs. "There's something else. I don't know how they do it, but they can communicate with one another over long distances. That made them very useful for military purposes. "They are loyal to one another, too. They try to protect each other and keep one another from being captured. Do you find that surprising?" The question caught Jordan unprepared. "Well, yes. It is, kind of--" he said. "They are only machines." The chief closed his eyes for a moment. He seemed tired. "Yes," he repeated, "they are only machines. Anyway, we don't know everything about them, even yet. There are still a few secret angles, I think. The men who could tell us are either dead or in hiding. "There's one fact though that gives us a great advantage. Their brain"--he stopped on the word and considered it--"I mean their thinking apparatus gives off a very penetrating short-wave length radiation which you can pick up on your meters anywhere in a radius of two thousand miles, and you can locate the source accurately if you get within fifty miles. "The only real problem you'll have in finding them is the confusion created by illegal atomic piles. You'd be surprised how many of them we have turned up recently. They are owned by private parties and are run illegally to keep from paying the tax on sources of power. You have to track those down, but once you get them labeled it will be clear sailing." He stopped to take a few puffs on his pipe. "Don't try to be a hero," he said after a few moments. "Don't get close to the thing you are hunting. None of them yet has injured any of us, but if one should want to, he could crush you to death with two fingers. Use the permallium nets and net bombs if you locate him." He tamped his pipe out. "Well, that's it," he said. The new man arose. "I want you to know that I appreciate the trust you have put in me." "Sure, sure," the chief said, but it was not unfriendly. "Do you like the job?" "It is a great opportunity," Jordan said, and he meant it. "What do you think about what we do to them after we capture them?" The new man shrugged. "I suppose it's the only thing to do. It's not as though they were human."