The proposition involving the science-fiction hero who captures the enemy device, brings it home, copies it and puts it into production is being abandoned in modern stories. But the actual difficulty of such a problem is always interesting and worthy of consideration. Only recently has Earth's own technology reached the point where such copying is not possible; today it is definitely impossible in a large field of devices.
Let's first consider this situation: time About 1920. Place: An American Army Air Base. Action: high overhead a small airplane tears across the sky with a high, thin whistle. Ground observers, after tracking it for a minute or so - during which time it has passed out of sight - report incredulously that it was doing between nine hundred fifty and one thousand miles per hour. It circles back, slows abruptly as the whistle dies out, and makes a hot, deadstick landing. Investigators reach the cornfield where it landed, and find it ninety percent intact - and one hundred percent impossible. Swept-back wings, no tail, automatic control equipment of incredibly advanced design, are all understandable in so far as function intended goes. But the metal alloys used make no sense to the metallurgists when they go to work on them. The "engine" moreover, is simply, starkly insane. The only indication of anything that might remotely be considered an engine is a single, open tube - really open; open at both ends. But the empty fuel tank had tubes leading into some sort of small jets in that pipe. The athodyd being unheard of in 1920, the thing is senseless. Filling the fuel tanks simply causes a hot fire that must be extinguished quickly to prevent burning out the tube. The fact that this is a guided missile intended for launching from a four-hundred-mile-an-hour bomber makes the situation a little difficult for the 1920 technologists; the athodyd won't start functioning below two hundred fifty mph, and nothing on Earth could reach that speed in 1920.
Meanwhile, the Signal Corps experts are going equally chittery trying to figure out the controls. First off, the plane's markings were clearly an advanced United States Army design. Many equipment parts bore United States Army Signal Corps markings and serial numbers. But the equipment inside is not only of advanced design, it's of meaningless design. The idea of printed circuits is fascinating, but understandable if not reproducible. Pentode amplifiers the size of a peanut are fascinating, not reproducible, and only vaguely understandable. For one thing, the filament isn't used at all; an indirectly heated cathode is a new item to them. However, the items that really stop them are several varieties of gadgets, all about the same size, but of violently different characteristics. There are units one eighth inch in diameter by about three fourths long which have resistance varying from one hundred to ten million ohms. Incredible, but true. Others have infinite resistance, and are condensers of capacity so high for their tiny size as to be unbelievable. Still others have three leads, and, opened, seem to be crystal detectors - understandable - but are amplifiers, which doesn't make sense. They also turn out to be non-reproducible. They are simple mechanical structures, using the very unusual element germanium, in the crystals. But the chemical expert's best purified germanium won't work when a reproduction is tried (you've got to have the right amount of the right impurity introduced in the right way. Techniques in the '20s weren't up to it).
Furthermore, there's a tube that's obviously a triode oscillator, but the frequency involved is so high as to be detectable only when using crystal detectors from the plane's own equipment. The circuit, too, doesn't make sense to the radio engineers, though the physicists from the Bureau of Standards finally figured it out (it's a tuned-line oscillator operating at about four hundred megacycles. The physicists had to go back to Hertz's original work with tuned-rod oscillators to get a glimpse of what went on). They can't reproduce the tube, and no tube they can make will oscillate in the circuit used.
Finally, there's another group of equipments they've simply agreed to forget. It seems to center around a permanent magnet of fantastic power which embraces a copper block drilled with holes of odd sizes, having a central electron-emitting rod through it. The magnetron is bad enough - obviously beyond reproduction, since the cathode can't be duplicated, the magnet can't be duplicated, and the metal-to-glass seals are beyond any available technique. But the associated equipment is worse. There is a collection of rectangular pipes made of heavy silver-plated copper. The pipes contain nothing, carry nothing, and appear totally meaningless. This time the physicists are completely stumped (wave-guide theory is a recent development; without some basic leads, and understanding of the order of frequencies involved, they'd never get there). And worst of all, the physicists find that several bits of the equipment contain radioactive material. They know about radium, uranium, thorium, et cetera. But - this is highly radioactive, and it's cobalt. But cobalt isn't radioactive! But this is, and it is cobalt (it's the transmit-receive tube; the radio-cobalt is used to keep it ready to ionize easily and instantly). They also find radioactive emanations from much of the plane's material, with faint indications that half the elements in the chemical table are radioactive - which is arrant nonsense (the guided missile had been flown through the fringes of an atomic bomb test gathering report data)!
In summary, the aerodynamicists report that the tailless monstrosity is interesting, but the principles of its design are confusing. The engine group report the "engine" so-called, can't be the engine. It was thought for a while that it might be a rocket, but since both ends are, and always were, wide open, it can't possibly be a rocket. The radio experts of the Signal Corps agree that some of the equipment is an immeasurably advanced type of radio apparatus, but the design is so advanced that it is futile to study it. It can't be reproduced, and involves principles evidently several centuries ahead of the knowledge of 1920 - so advanced that the missing, intermediate steps are too many to be bridged. The mystery electronic equipment, called Equipment Group X, remains simply mysterious, save that, in some way, it involves a receiver operating on an unknown, but very high frequency (by which they meant not the ten thousand megacycle input but the "low" frequency intermediate frequency amplifier, operating at only thirty megacycles. Having no means of generating thirty megacycles at that time, they could only say it was higher than the highest available. And they didn't, of course, recognize the ten kilomegacycle RF head as a receiver at all).
The physicists would be inclined to ascribe it to Mars, Venus or any other non-terrestrial planet, if it weren't for the obvious Signal Corps markings. Since terrestrial cobalt isn't radioactive, and the cobalt in this ship is.
But anyway, the reports can only be tucked in the "File And Forget" division. About the only thing they can lift out of that piece of marvelous equipment is the secret of making good, small, high-resistance electronic resistors. The chemists and physicists did crack that one, and it's the answer to an electronicist's prayers; the tiny resistors are not wound with sub-microscopic resistance wire, as was at first believed - they're little ceramic tubes filled with a composition of clay and graphite which is such an extremely bad conductor that it does the job beautifully. By varying the composition, resistors of a standard size can range from one ohm to one hundred million.
At that, our 1920 group was really lucky. Suppose the item that fell through a time-fault had carried an atomic warhead. If it didn't go off, it would have presented the physicists with two of the most dangerous, utterly inexplicable lumps of matter imaginable. Pure U-235 or pure plutonium - that would have driven the chemists mad! - before they'd even discovered synthetic radioactivity. They would have been certain to kill themselves by bringing those two masses too close to each other, though, out of the bomb mechanism, they wouldn't have exploded.
But - write your own ticket, in your own special field. Let 1920, or 1910, or 1890 try to understand the functioning of any one of your modern gadgets. Even though, in those years, first-rate scientists with a full understanding of scientific methodology, and with fairly complete laboratory equipments, were available!

November 1948

END