Judging by the folk epic, this knife has existed for quite a long time, in any case, most of the models were released somewhere during the Second World War and immediately after it. There are many people who have seen this knife, there are detailed descriptions of the design and its combat capabilities, but the trouble is, when you start to understand, everything turns out to be not so simple.
So eyewitnesses for some reason begin to refer to friends or acquaintances, to their grandfathers, who went through the whole war with such a trophy knife, to the special forces who fought with him in Afghanistan or elsewhere.
But none of the narrators, alas, for some reason did not see such a knife himself. Or met in early childhood, but did not hold it in my hands. Or he almost held it, but did not use it, since the owner treasured it and did not give it to anyone. When asked where, this knife is now and whether it is possible to look at it, the answer follows: it was a long time ago, and then the knife disappeared in the most strange way, well, what can I say, this happens with valuable things. Whether they saw it or not, they held it or not, they used it or not, but such storytellers know everything about the mercury knife and are very willing to share exclusive information.
I will try to list the signs of a "real" mercury knife based on these stories. First, the knife is usually classified as a "German Finn", at any rate. "Eyewitnesses" that came across to me personally. If you ask an “eyewitness” to draw a knife he has seen from memory, then with a probability of 99% he will draw an ordinary Finn with a guard or something bayonet-shaped, while he will certainly complain about bad memory and inability to draw. The design is also clear: all "experts" claim that there is a channel in the blade, mercury is poured into it, which gives the knife magical possibilities (I wonder how they saw this channel - it's inside). The main feature of the product is that it does not matter how you throw such a knife, it will still stick right into the target. Then there are options for throwing distance. If modestly, then it is 7-8 meters, and if in an adult way, then all 10-15.
Having disassembled this tale by the bones, it becomes clear that such a miracle as the "mercury knife" does not exist in nature, and its appearance is the fruit of idle fantasies, like the famous "Red Mercury". But there is no smoke without fire. If you dig, then such enduring legends are often based on real events, or almost real ones. True, the question arises: "Why?". Indeed, why fence a vegetable garden. Throwing a knife is not rewarding. Tell any expert about throwing a knife, and he will look at you like an idiot. To take and throw away your last weapons in a critical situation - well, this is not of great intelligence. Even with a successful hit, the chance to incapacitate the enemy is minimal.
The knife is not a bullet, it does not have a stopping effect, at an extremely small distance they need to hit the vital organs of the enemy, and this is quite difficult. It only happens in the movies. Nevertheless, in the terms of reference for the development of combat knives and now there is a criterion - "the possibility of throwing a knife." But here the military consider not so much its combat capabilities as a throwing weapon, but rather the strength characteristics that allow the knife to withstand such use. That is, throwing a knife on tests is nothing more than a test of strength. At the same time, no one seeks to throw it so as to hit the target with a blade. They threw it three or five times with all the dope, remained intact, well, great. But that is why any nonsense is good, that it is very tenacious. There is also a legend about the knife as a throwing weapon.
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It is clear that learning to throw a knife is hard and time-consuming, and the result is ambiguous, therefore inquisitive minds make every effort to simplify this task. It is likely that one of the ideas that theoretically should have helped in this difficult matter is just the idea of a "mercury knife". Its essence is as follows: there is a cavity in the blade, in it there is a heavy liquid or a loose, but heavy substance. Mercury is almost ideal for the role of such a liquid. When thrown, it rushes into the front of the knife and, as it were, drags it along, stabilizing it in flight. So much for you one hundred percent hitting the target, like a spearhead. Nice, but hardly feasible in practice.
Let's take the very "mercury finca" sung in folk ballads. How thick is the blade? 4-5 mm. Where is there a channel for mercury to do? A hole with a diameter of 3 mm will not work anymore - and how much mercury will go there? As in a thermometer or two … In this case, do not forget that mercury must still be able to move in order to gain a certain speed. Therefore, the remaining volume for its placement will be even less. That is, the inertial mass itself is very small. And how does the resulting mass of mercury relate to the mass of the knife itself? No way. Such a mass is small for real stabilization. You can, of course, torment the reader with calculations, formulas and all sorts of tricky terms like the moment of inertia, but I will not do this out of philanthropy.
By the way, air also interferes, for such a small channel diameter it is critical. In some scientific works, where theorists describe the "mercury knife", it is advised to pump out air from the cavity. The advice, of course, is valuable, but technologically it is rather complicated and expensive. Well, okay, suppose that, courageously overcoming all the difficulties and mistrust of retrogrades, the air was pumped out, mercury was poured, the knife is ready for use. So what? Nothing, because the most beautiful "mercury knife" still needs to be able to throw. If there is a whip of the brush during throwing, then do not expect any stabilization either in theory or in practice. And the effectiveness of any throw depends only on the physical capabilities of the thrower and his preparedness. The knife itself will not fly.
Let us repeat - there is still some truth in the legend of the "mercury knife". To clarify, you will have to digress a little from the topic of knives and go down into the depths of the sea. For spearfishing, when shooting at long range, it is important to have a large mass of the harpoon. Those hunters who adjust spearguns themselves sometimes use weighted harpoons, made like a tube filled with mercury. Such a harpoon has excellent combat properties, since a double blow occurs when hit. First, the harpoon itself hits the target, then the mercury located in its cavity inflicts a blow, as if further driving it into the obstacle.
This design prevents the harpoon from bouncing off the obstacle and increases its penetrating ability. With what force this blow was delivered, it became clear when such a harpoon missed and hit the stone. The tip, made of durable steel, literally twisted into a ram's horn. This is the effect allegedly used in the "mercury knife". But this is just a theory. To use this effect, the usual design is simply not suitable. A good ratio of the mass of the movable inertial body to the knife itself is required. That is, the lighter the knife and the greater the mass of the inertial body, the greater the effect.
If we take an ordinary combat knife as the basis for the design, then it is very problematic to place such a body in its dimensions. Therefore, in practice, the "mercury knife" looks like a very simplified design. It is a tube with a sharp tip, of a fairly large diameter, with fairly thin walls. Since there are many problems with mercury, it is easier and cheaper to replace it with fine lead shot mixed with lubricant. Here you will find ease of manufacture and good sliding inside the channel of the blade - there is no need to fiddle with vacuum and sealing. In addition, mercury is thought to be poisonous. There is, of course, a difference in mass between mercury and small fraction, but it is not fundamental.
By the way, shot filling is used in inertial hammers, where it justifies itself, besides, ideally, you can use not lead, but tungsten. Therefore, in fact, such a knife is correctly called not mercury, but a knife with an inertial body. This design can provide maximum throwing efficiency and is easy to manufacture. When hit, the "mercury knife" has a lot of energy and provides a significant probability of being hit in especially difficult cases, for example, when it is necessary to inflict a defeat through warm clothing, or when the knife hits a large bone. Such a knife does not have any special stabilization - if the throw is made with errors or poorly, no inertial body will help you. So the real combat effectiveness of any throwing knife does not depend on the knife, but on whose hands it is.
Now another question: who makes or produced mercury knives? Indeed, the first thing that comes to mind is that knives are designed and produced for some sovereign structures. Who else needs an effective silent weapon - of course scouts and saboteurs. But ask any scout, he, of course, heard about mercury knives, but he never saw it alive, at best he was taught to throw an ordinary combat knife. The reason is simple, the "mercury knife" does not guarantee 100% silent destruction of the enemy, even silent firearms do not guarantee this.
Therefore, no one will develop a complex universal design for the sake of an ephemeral increase in throwing efficiency. The only real application of this design is to solve the problem of increasing the energy of a piercing blow. Here the inertial body may well be used, but not in the blade, where there is simply no place, but in the handle. Such a handle can be made in the form of a tube with a stopper. That is, any owner of a survival knife, having poured shot or a gulf of mercury into his hand, can become the owner of a mercury knife, more precisely, a knife with an inertial body.
Thus, it is possible to preserve the parameters of a conventional combat knife and increase its effectiveness without much complication of the design. Most likely, a similar design lies in the legends about "mercury knives", although there is no documentary evidence of the existence of such knives. Perhaps there were such developments, the special services love any exotic, and sometimes from their notions the hair of a normal engineer stands on end. But, most likely, things never went beyond the prototypes, leaving in the memory of the folk the legend of the ghost weapon. An indirect proof of the inefficiency of such a design is the fact that the post-war samples of throwing weapons were developed according to a different principle, although the effectiveness of such models was also questionable.
However, low efficiency does not always serve as a guarantee against the appearance of such models in service. Soviet special services used throwing folding shurikens. The idea is quite reasonable, since the probability of defeat really increases. But the problem was different: to carry with you a throwing "star" weighing almost half a kilo is a pleasure below average. It is easier to use a sapper blade for throwing. The efficiency is not less, and the versatility is much more. You can even dig with it. The Poles went even further, for some reason they invented the Agat knife, in which the capabilities of an ordinary and a throwing knife were combined. The name of the knife is beautiful, as a demonstration of the developer's ingenuity is quite suitable, but as a real weapon it is too complicated. However, the constancy with which such constructions appear testifiesthat the irrepressible fantasy of mankind will not dry out soon. Although such knives have no practical value.
All this led to the fact that the use of a knife as a throwing weapon was actually abandoned. Samples of combined weapons appeared, in which the force of the hand was replaced with a spring. Unlike the legendary "mercury knife", spring-loaded shooting knives did exist in real life, although they were not particularly effective. This idea also turned out to be far from perfect and had a very narrow range of applications, but the spring knife has a definite plus. This is great hitting accuracy. However, this is where the pluses end, and the legends begin again … For spring-loaded shooting knives, folk tales usually increased the firing range. Say, 25-30 meters is a distance at which, having such a knife, you can destroy any enemy. And here, too, there is some truth.
When firing from such a knife, the blade really flies about 20 meters (here it is already up to 25-30 meters not far away, you just need to be able to measure, and if at this distance the blade stuck into the nearest fence, then here is information for another legend). But this is the range of its flight, not the range of destruction. The distance at which you can actually hit the target with such a weapon is much more modest - only 5-7 meters, at such a distance the blade retains sufficient energy. (The main source of information about shooting spring knives is the book "Aquarium", written by the traitor to the Motherland Rezun, hiding under the pseudonym Suvorov, in any case, the "experts" with whom I had to talk about this knife referred mainly to this "indisputable authority". Although the description of special equipment and weapons given in this book, to put it mildly,do not always correspond to reality). Later, with the invention of silent ammunition and the creation of LDC and LDC-2 knives under them, this weapon finally lost its niche …
I've always wondered where these myths come from. I think each of us tried to throw knives, and, of course, few people succeeded right away. To console oneself, it is generally accepted that for throwing, knives need special, somehow cunningly balanced, with mercury in the blade and other tricks. In fact, you just need to be able to throw. There are sports sections where they teach how to throw knives.
They hold competitions and participate in knife exhibitions, where they show their skills and explain to everyone the basics of throwing knives. They have no mercury knives, but the most common ones, which they throw with enviable accuracy from various distances. The only difference is that they make their knives strong so that such a knife can withstand maximum loads.
Those. they do not have overlays on the handle, the thickness of the knife is 3.5-4.5 mm, there is no cutting edge (i.e. the knife is not sharpened) so as not to injure the hand during training. There are videos showing their trainers throwing nails, ballpoint pens, screwdrivers, different kinds of knives, forks, side cutters, metal diamonds and a lot of other objects that are absolutely not suitable for throwing. This skill is mesmerizing.
So, as the popular wisdom says, "there is no need to produce essences where they do not exist." Throwing knives requires straight arms and good coordination, not special super knives. And for the removal of sentries and other similar tasks, there are much faster and more effective methods than dastardly mercury poisoning.