This is a work in progress. The contributor has made efforts to make sure that information is correct, but inevitably there will be errors that require future correction.
What makes the katana special?
A traditionally made Japanese sword (the katana is a Japanese sword, but not Every Japanese Sword Is a Katana) is defined by three things: being made of tamahagane steel, smelted from iron-rich sand in a large clay furnace called a tatara and folded several times to form a layered billet; being of laminated construction, of which the most common version—the kobuse-style—is a high-carbon outer "skin steel" (kawagane) wrapped around and forge-welded to a low-carbon inner "core steel" (shingane); and being differentially hardened. Differential hardening is performed by applying insulating layers of clay to the blade, which are thicker on the back than on the edge. The coated sword is heated to a high temperature and quenched in cold water, so that the edge cools rapidly and gets set into a very hard crystaline structure called martensite, while the slower-cooling sides of the blade become not-quite-so-hard pearlite, and the core and back of the blade comprising the shingane remain relatively soft and pliable. The pattern in which the clay is applied will determine the appearance of the hamon, a cloudy pattern showing the boundary between the hardened edge and the softer body of the sword. Differential hardening is also what gives the blade its curvature: unlike a curved sword made from a homogeneous piece of steel, which is forged in a curved shape before heat treatment, the Japanese sword is forged almost straight and actually bends itself into a curved shape when it's quenched because the edge and the body have different masses and cool at different rates. Tamahagane is basically a kind of bloomery steel. The ore smelted in the furnace comes out as a porous mass of iron and slag called a bloom, or in Japanese, the kera. It is a highly impure and heterogeneous raw material, and when the kera is broken up the tamahagane is sorted into several grades based on the pieces' quality and carbon content. Swordsmiths try to select the best pieces for their needs, flattening them into plates, stacking them, and welding them together to make a billet. The repeated folding of the billet is necessary to remove impurities, homogenize the distribution of carbon, and reduce the overall carbon content to the desired level for the shingane and kawagane, respectively, since the more times the steel is heated and folded, the more the carbon level is reduced. It is possible to overdo it, and a billet should only be folded 8 to 16 times. Since the number of layers is doubled every time you fold it, over 16,000 layers are produced by folding only fourteen times. While the traditional process is quite effective at removing slag inclusions and evenly distrubuting the carbon when performed by a skilled smith and apprentices, it is obsolete and inefficient compared to modern industrial processes which produce better steel in greater volumes and with more consistency. You cannot get any benefit out of folding a piece of modern manufactured high-carbon steel, because it's already as homogeneous and pure as it's ever going to be. Folded tamahagane is still used in sword making today not because it's somehow "superior" to modern steel, but rather because it's valued as a historical tradition, and because it gives the sword the prized aesthetic effect of a grained surface pattern. The Japanese were far from the only culture to make swords out of bloomery steel, or to fold the billet to make patterned blades. Even the Europeans did it at one time! The Japanese just happen to be the most famous, and to have turned it into a very refined art. And for what it's worth, it worked pretty well for them. Metallographic analysis of historical katana blades show that the fancy ones, at least, were quite structurally sound. Not all katana were well-made, of course, but neither were all swords produced by other cultures, either. And since it was back in the days before precise instruments like thermometers or modern knowledge of physics and chemistry, it was difficult to achieve consistency or for anyone to know exactly what they were doing. If you look at measurements from surviving sword blades of the Middle Ages and Renaissance, the number of slag inclusions, the percentage of carbon in the steel, and the rate of successful heat treatment is all over the place, just as you'd expect. Comparing the metallurgy of Japanese blades with those of other cultures is frightfully complicated; the short of it is that the Japanese way isn't the only way to make good sword steel, and other, more modern methods may be a lot easier, but it's still a pretty impressive process, and it works. In contrast to the smelting and folding, which today are retained mainly for historical and aesthetic reasons, lamination and differential hardening do still have a functional purpose: they allow the sword to have a very hard edge—often with a Rockwell hardness of 60 HRC—which can hold its sharpness very well. If the sword were that hard all the way through, it would be very brittle and therefore likely to snap; in comparison, historical European swords are more often 45 to 50 HRC at the edge. It is often said that the tougher and more pliable back of the blade acts as a shock absorber to prevent the edge from taking damage, but this is actually incorrect; if the edge hits something that causes it to chip, there's nothing the back of the blade can do about it. What it does ensure is that a chipped edge will not spread into a fracture that compromises the entire structure of the blade, causing it to snap. Any trauma that can chip the edge will cause the rest of the blade to take a bend, rather than snapping off. Also, one explanation of the purpose behind the pattern of the hamonnote is that it helps to limit damage to the edge. Early Japanese swords had straight, narrow hamon, but supposedly this sometimes resulted in the edge delaminating from the body upon impact. The solution devised during the Heian Period was to apply the clay to make a wavy or irregular hamon, and to add thin clay lines called ashi across the edge which would leave unhardened lines separating the edge into compartments. The wavy hammon would act like a zipper keeping the edge mated to the back, and the tooth-like patterns would ensure that any chip was confined between two ashi, sparing the rest of the edge. A "through-hardened" blade made from one homogeneous piece of steel cannot be made quite as hard-edged and will tend to dull more quickly, but has the advantage of durability. The hard yet brittle edge of a katana is more likely to chip if struck against something too hard and unyielding, such as the edge of another sword, which is why many parrying techniques in kenjutsu use the sides and back of the blade instead of the edge. Meanwhile, the blade consisting of a hard edge mated to a softer spine is more likely to take a permanent bend or twist if exposed to lateral force, taking a set from the kind of bending that a through-hardened blade would be expected to spring back from. A severe bend can interfere with technique and cutting performance until corrected, which would have been difficult in the heat of battle in the days when they were used as weapons, though at least this was better than a blade that had totally snapped. On the other hand, this same softness makes a bend easy to correct with the right method, whereas if a through-hardened blade is bent far enough for it to take a set, it will be harder to straighten out again than that of a katana. This is just one example of how the katana is not categorically superior to other swords, and whether or not it will serve you better than a different type of sword depends entirely on the context in which you're going to use it.
Origins of the Myth
Why do a lot of people seem to think the Japanese sword is superior? For the Japanese it's understandable that they'd want to brag about their swords being the best, but much more remarkable is the fact that people from all over the world seem to believe them. There are many possible explanations for this state of affairs, and the following are just a few suggestions. One reason is Older Is Better: the notion that the craftsmen of olden times had secret knowledge that has been lost to modern craftsmen. Since Japan has a relatively continuous tradition of swordsmithing which goes back to the middle ages and lives on today, it can be said that they still make swords very similar to the old ones. Japan's status as an island nation and the "closed country" policy of the Edo period also meant that their sword making tradition was less "diluted" by influence from their neighbors, thus encouraging gradual evolution rather than disruptive revolution and preserving its distinct national character. The various governments of Japan since feudal times have also helped to foster the craft of sword making and preserve its history, culminating in post-war Japan's laws regulating the manufacture, import, and export of swords while protecting the best antique swords as national treasures and important cultural properties. Admittedly, Japan has sometimes had periods of war and disruption which interrupted or destroyed certain sword traditions, such as during the Meiji Restoration when the samurai class was abolished and the wearing of swords outlawed, thus putting many of the old-fashioned swordsmiths out of work. Still, their sword culture is more completely preserved than other Asian cultures that went through more prolonged cultural and technological upheaval, and is in a totally different league from Western Europe's Medieval and Renaissance traditions, which had to be resurrected after completely dying out. Although the first revivals of old European weapon-making and martial arts began in the 19th century, it was not until the rise of the internet around the turn of the millennium—accompanied by the publication of more translations of primary sources—that European sword arts really began to take off. Compared to Japan's traditional culture, which places more emphasis on tradition and basing present practices on the knowledge of one's ancestors, Western Europe has long been focused on the idea of progress and each generation being better than the last. The writers of the Renaissance and the Enlightenment created the idea of the primitive and superstitious Middle Ages because they thought they were so much better in comparison, and while they idolized the greatness of classical Greece and Rome, they nevertheless felt like they could build upon and surpass the achievements of the ancients. Despite the fact that there were always proponents of the Good Old Ways who resisted newfangled sword designs and fencing styles, each time they were ultimately drowned out by the embracers of change and improvement. While many swords associated with saints, nobles, and the like were preserved in churches or princely collections, they were not considered as templates for future generations of swordsmiths, and tended to be valued more for their history than for their intrinsic qualities. Contrast this with Japan, in which Kotō (古刀, "old swords") from around 900–1596 were considered the best and imitated by later swordsmiths, while the succeeding Shintō (新刀, "new swords") made from 1596–1780 were considered lower quality in comparison. Meanwhile, the teaching of medieval styles of fencing in Europe died out as the weapons they were based on went out of fashion, and many of the fencing manuals preserving these teachings sat forgotten in obscure libraries until the aforementioned Internet Age revival. This general unfamiliarity with the old tools allowed later writers to conjure up the pervasive myth of medieval swords as being dull, twenty-pound bars of iron that prevented any kind of sophisticated technique, an extreme contrast with how Europeans would soon percieve the swords of Asia. The first visit to Japan by the Portuguese in 1543 began the Occidental World's relations with Japan. From the beginning, European visitors were impressed with the cutting ability of the Japanese sword, and brought back some hair-raising tales of beheadings, encounters with fierce pirates, and the like. Naturally, some fine swords entered European collections as diplomatic gifts. The isolationist policies of the Edo period limited the amount of direct contact beteen Japanese and Europeans, but by the mid-19th century Japan was forced to sign treaties that opened her up to the West again. This is when Europeans started forming many of the opinions about Japanese swords that the have today. The European sword industry was nothing to sneeze at, mind you, and was especially distinguished by its access to good steel and ability to turn out large numbers of blades that were of at least decent quality. As early as the 16th century, Indian weapon makers were importing blades from manufacturing centers like Solingen, Germany so they could hilt them in the native fashion. The best Indian bladesmiths could make blades that were a match for anything in the world, and none of them were in danger of losing their jobs, but it was the "budget" market that got displaced by the European imports; for the same price as a crappy Indian blade, you could get a munitions quality blade from Europe that was a bit nicer and much more reliable. By the 19th century, especially after the adoption of the Bessemer process, Europe was awash in high quality, affordable steel. The downside to all this innovation was that the sword makers in the meantime had lost some of the traditional wisdom going back to the middle ages, and in some cases ended up having to reinvent the wheel. For example, scabbards made entirely out of steel had become common because of the need to mass-produce them, and also to make them durable since they would be taken on campaign by conscripts who didn't know the finer points of sword care and were likely to treat their swords and scabbards roughly. A wooden core was an additional expense, so they were often left out. Unfortunately, it turns out that wood is very good for preserving a sword's sharpness, while being kept in metal alone makes them dull really fast even if they've just been sharpened. British soldiers on colonial assignment were often frustrated that their swords would already have become dull within a couple weeks after sharpening, while their Indian and Japanese counterparts always seemed sharp and ready. At the time, the British were just as impressed with the Indian Talwar as they were with the katana, but for some reason that fact seems to have been forgotten by pop culture. European armies were also affected from time to time by a bad batch or some experimental new pattern that turned out to be a failure. Blades that weren't thick enough or that were tempered to be too flexible could fail to thrust through an opponent's greatcoat. There must have been quite a bit of envy, and a sense that the Indians and the Japanese knew something they didn't. There may have also just been something deeply romantic about feudal Japan that orientalist Westerners admired. They were in the throes of industrialisation, and society was changing so fast that it seemed scary and alienating. Therefore, when Europeans finally got a good look inside Japan it looked to them like a land in Medieval Stasis where they saw their own past reflected as if through a skewed mirror. The people lived under a social order that resembled the structure of European feudalism, with lords living in castles and peasants working the land; the culture supported all kinds of traditional arts and crafts permeated with spirituality and appreciation for beauty; and there were samurai warriors who seemed to practice a code of conduct like that of medieval knights, whose Martyrdom Culture and embrace of Honor Before Reason appealed to the romantic side of Romanticism Versus Enlightenment; and of course, the government had established the closest possible thing to Fantasy Gun Control by disarming the population, while enforcing Heroes Prefer Swords by making the daisho the samurai badge of office. Despite the similarities with European history, everything there was so thrillingly foreign, oriental, and exotic, and there was enough Values Dissonance between the two cultures to generate a lot of interesting drama. This combination of the familiar and unfamiliar contributed to the great fad of Japonisme, the fetishization of all things Japanese. Of course, no sooner had the West gained unfettered access to Japan than the highly conservative social order was already in danger of collapsing from both internal and external pressures, to be replaced in the nationalist and modernizing Meiji Restoration. The samurai were a dying breed, and occidental observers sighed at their passing in much the same way that they lamented the passing of the Noble Savage who once roamed The Wild West. The romanticized spirit of the samurai which the katana is said to embody is undoubtedly part of the reason it appeals to Westerners so much. The folding of the steel billet and the construction of the sword through lamination is always a major source of mystique for the Japanese sword. People tend to assume that the more handcrafting goes into something, the better the result will be. In many cases, such as the hand adjustments to make a hilt and scabbard fit a blade, this really does make a big difference. However, the invention of better smelting and steel-making technologies has reduced the amount of work that a swordsmith has to do in order to prepare the blank, and the raw material is often of better quality. We should consider, here, that what is most beautiful and what is functionally superior are not always the same thing. Many of the traditional processes are indispensible for creating the aesthetic qualities for which the katana is most loved, and fake effects such as a wire-brushed hamon are always easy to see through. It takes a certain amount of work to make something functional, but an amount of work far above and beyond that is needed to give it that kind of beauty and character. For some strange reason, people seem more willing to believe exaggerated stories of the katana than sword myths from Western cultures. While chivalric romances often feature heroes cutting their plate armored opponents from the crown of the helmet down to the saddle, nobody would mistake this as thing that actually happened. In contrast, stories about Japanese soldiers cutting off machine gun barrels during World War II circulate the internet as urban legends.
Pros and cons of the katana
In contrast to the tachi, whose shape and method of wear indicate it was more designed for use on horseback and in armor, the katana was more of an infantry sword and suited to civilian clothing as well as fighting in armor. It is certainly well-suited for the quick-draw and attack that are required in self-defense situations, codified in the practice of iaido: in the first place it is worn edge-up, thrust through the sash, so that one can quickly grasp the scabbard with the left hand, and immediately draw and cut with the right. The long hilt is wrapped in rayskin and silk cord for a good grip, and has only a relatively smallnote disc-shaped guard (tsuba) without any knuckle bow or bars to hinder one from quickly grasping it. A brass fitting called the habaki, wrapped around the base of the blade right where it meets the tsuba, fits snugly inside the mouth of the scabbard when the sword is sheathed and is essentially the only thing that would keep the sword inside if you turned the scabbard upside down and shook it: as soon as you free the habaki by flicking up on the guard with your left thumb, or even just by squeezing the mouth of the scabbard, the rest of the blade slides right out with no resistance. That quick draw and ease of wearing it comes at a price, however. Compared to European swords with a cross guard, side rings, or basket hilt, the simple circular tsuba offers less hand protection. Also, katana tend to be relatively short-bladed for swords with two-handed grips. The length of a Japanese sword's blade—excluding the tang—is the nagasa, a measurement based on an imaginary straight line drawn between the sword's point and the mune machi, a notch at the back of the blade at the top of the tang. In other words, nagasa refers to the naked steel that isn't covered up by the handle. By modern defnition a katana is a blade of at least 60 cm (23 1⁄2 inches), while those exceeding 90 cm (35 7/16 in) are called odachi ("great sword") or nodachi ("field sword"). More often than not, historical katana have a nagasa of less than 76 cm or 30 inches. In comparison, European longswords tend to be more like 35 to 40 inches (89-101 cm) in the blade, rapiers 40 inches or more, and even most one-handed sabers of the 19th century had more than 30 inches. Nodachi could have blades of up to 130 cm, but we'll stick to discussing the katana. On one hand, a short blade makes the typical katana handier in the close quarters of mass battle or indoor fighting, and is easier to get out of the scabbard quickly than a longer-bladed sword such as a rapier. On the other hand, an opponent with a longer weapon can give the katana-wielder a hard time if he has enough room to take full advantage of his weapon's reach, particularly in thrusting play. However, the reach disadvantage is not as great if we compare cutting range. A rapier or an acutely tapered longsword has a bodkin-like point which is not well-shaped for cutting, and the center of percussion or "sweet spot" for cutting is quite a bit further back due to the blade's cross section and the point of balance being closer to the hand. The katana is relatively forward-balanced and has a broad hatchet point suitiable for tip cuts, so the range of an effective cut could be greater than or equal to one made with a rapier or a tapered longsword. The katana basically deserves its reputation as a particularly fearsome cutter. The long, two-handed grip allows the sword to be wielded with power and control. According to Matt Easton, the curved shape and stiffness of the blade make it relatively forgiving of a beginning cutter's technique; In comparison, it actually takes a lot of skill to cut cleanly through a tatami mat using something like a sharply tapered Western longsword, since you need to have perfect edge alignment and hit using the center of percussion. Other cutting basics are similar for both: As Keith Larman explains here, cutting well requires that one both use a proper slicing motion and maintain a straight path throughout the cut, as introducing rolling or twisting motion at any point during the cut will create drag and put more stress on the edge. Because of the katana's unique hard-edged construction, however, edge durability is a particular concern. An acute edge of the type found on a hira zukuri style blade—one whose cross-section is a simple wedge shape with flat sides—can be made very sharp and is effective at slicing through soft targets such as human flesh and thick layers of cloth. Indeed, most tanto and some wakizashi had this kind of cross section. However, most katana from the age of the samurai were shinogi zukuri, a style introduced sometime during the second half of the 10th century which features a shinogi or beveled ridge running down the length of the flat on each side. Many blades also had a generous amount of niku or "meat" to them, meaning that the surface between the shinogi and the edge bulged out somewhat instead of forming a flat plane. While the edge of this kind of blade would be less acute and therefore not quite as razor-sharp, there was more material to support it in case of an off-angle cut or impact against something hard, like armor or another blade. A blade with a lot of niku will also produce less drag than a flat-sided blade while cutting through thicker and heavier targets, since it has a way of parting the material as it passes through while minimizing the amount of the blade's surface area in direct contact with the material. One might say that blades had to be somewhat overbuilt back in the day, since the quality of the steel and of the heat treatment was often unreliable. An acute-edged hira zukuri katana might have been in danger of snapping in the old days, but the durability risk of making a katana-length hira zukuri blade is far less significant if the smith takes advantage of modern materials and methods. In any case, one should not get the impression that the katana's impressive cutting performance is unequaled, since many swords designed for cutting such as European knightly swords, Middle Eastern sabers, and Chinese dao can achieve similar results in cutting tests. The fact that these blades are very diverse in shape and construction indicates that when it comes to designing a sword for performance, "there's more than one way to skin a cat". Also, in terms of stunts such as cutting thin sheets of metal or slicing bullets in half, closer inspection will often reveal it to be a Deceptively Simple Demonstration that any kind of well-made sword could do in the right hands and under the right conditions. It goes without saying that a katana cannot slice the barrel off of a machine gun or slice another sword blade cleanly in half, since sharpness is simply beside the point in that situation and no sword would be able to do it. While there are some exceptions, a good rule of the thumb is that if another sword can do it, the katana can probably do it, and if another sword can't, then the katana probably can't. A quick note about thrusting. The katana can thrust surprisingly well, despite having a "hatchet point" and despite being curved. In fact, the inherent stiffness of the katana (caused by the thick cross section and lack of springiness) is an advantage when trying to thrust through anything. Attacks with the point (kissaki) are a significant aspect of kenjutsu, and tests suggest that the sharp-edged point of the katana would have easily penetrated the human body, even through thick layers of cloth armor or clothing. The kissaki was perfectly adequate for seeking the weak spots in Japanese armor. It might not have been ideal for slipping through the gaps in European-style full plate armor or penetrating riveted mail the way a stiff and narrow knightly longsword or estoc would be, but since they did not encounter those defenses, it wasn't a problem. Presumably if they had faced such difficulties, they would have had to consider making changes. The hatchet point of the katana facilitates the use of tip cuts, so it had its advantages. In any case, the thrust remained secondary to the cut in Japanese sword technique, and while there were various point styles there was no pressure to dramatically change the shape of the katana to make it better at thrusting. The blunt spine of the katana is convenient for half-swording, which is done in many kenjutsu techniques in order to attack at close range with either the edge or the point. It is also technically possible to half-sword in the European manner by wrapping your hand around the blade—and do so without hurting yourself on the edge—but Japanese half-swording simply uses the hand to support the spine. The modular construction of the hilt is useful and convenient, but also relatively delicate compared to the European method of wedging the crossguard onto the shoulders of the blade and securing the pommel by peening the tang over it. The tang of a Japanese sword is secured inside the handle mainly by a very snug fit with the grip wood and a single wooden peg that passes through a hole in the tang, though copper pegs and/or a second peg are sometimes found on modern reproductions. This makes it possible for a Japanese sword's owner to disassemble and change the fittings with hardly any tools, unlike a European sword which has to be taken to a cutler for re-hilting. However, this reliance on the smooth fitting of handmade parts makes it more potentially sensitive to damage. The pommel is just a cap on the end rather than a hefty metal knob, and the tang does not pass all the way through the grip. And, as mentioned already, the katana is relatively forward -balanced and doesn't have as much mass concentrated in the hilt. Thus while the katana can make effective pommel strikes like other swords, the European technique called the "murder stroke—where the blade is grasped with both hands in order to swing the hilt like a hammer—would not be very advisable or effective with a katana. One simple reason that katanas might not be "better" in a modern situation is their price. As already mentioned, making a katana in the traditional way is extremely labor-intensive. This is why, according to Sword Buyers Guide, the starting price for a newly made katana from a licensed Japanese swordsmith is about 4,000 USD, with the average being closer to 7,000 USD; the best can cost up to 30,000 USD, and you can hardly ever order them online; you would probably have to go to Japan and prove yourself worthy of owning the sword! If you can't afford a bespoke sword made in Japan, there are cheaper alternatives from China. High-quality Chinese-made katana with folded blades come in the $1,000-2,000 range; you would not want to buy a folded katana for less than this, because the steel quality or forge welds are more likely to be defective, which would actually make it worse than a cheaper one made from mono steel. A decent, functional Chinese-made katana with a through-hardened mono steel blade can be bought for as little as $300, though you'll normally have to go above $600 to get high quality. The main sacrifice of mass-produced katana comes in fit and finish, especially regarding the tsuka (hilt) and fittings. And by Japanese law, a sword isn't a nihonto unless it is made from tatara steel using the traditional methods, so your mono steel Chinese-made sword technically isn't a "real" katana despite what the marketing may tell you. Also, there's maintenance. Regardless of whether it's a priceless antique or a relatively modest modern sword, if yours is traditionally made then you can't just polish it the way you would one of mono steel, but have to use more skill- and labor-intensive methods. Perhaps it isn't necessary from a purely functional standpoint, but you have to take it to a professional polisher if you want it to look its absolute best, which can cost upwards of $100 per inch. The performance differences between through-hardened and differentially hardened katana blades made in a similar shape are relatively minor: one thing that may be seen as a benefit is that a differentially hardened katana feels more "harminically dead" compared to a through-hardened one, meaning that the vibrations from hitting somewhere other than the blade's center of percussion are less pronounced, making it more forgiving of the user's technique. It can also have a slightly harder edge than a through-hardened katana. That doesn't mean that the maximum sharpness will be increased; if they're both freshly sharpened, then you won't get any measurable difference when cutting tatami mats. However, it does mean that the edge can remain that sharp for longer compared to a through-hardened blade throughout a day of cutting or after a long period of storage. As for durability, a through-hardened katana can spring back from abuse, whereas one should be wary of destructive testing on a traditionally made katana, lest it take a set or a twist that would be difficult to straighten out.