Katana are popularly conceived of as "the best" swords ever made. While they are certainly effective blades, much of their modern status over other sword types owes more to the entertainment industry than the realities of swordsmithing and combat. The swords, also known as "samurai swords" and loosely defined as curved, single-bladed Japanese swords with blades at least two feet long, have a variety of near-magical properties ascribed to them, often with little explanation given. There are, however, some rationales that are used to provide a basis for the swords' supposed prowess. Though these reasons may sound convincing, by and large, they are either inaccurate or misleading.
First and foremost, it is important to question the base assumption that there can be a single "best" sword, as it ignores the important question, "best at what?" Every sword made and used in every part of the world throughout history was designed in response to unique conditions and made for specific uses. Differences of terrain, available ore, enemy weaponry, armor, mounted or unmounted combat, and numerous other considerations have shaped every sword (and indeed, every weapon) ever made to attempt to be the best possible weapon for the given situation. No single sword design could ever be the overall "best," as any design will fail if placed in conditions far removed from those it was intended for.
Below are some of the most common rationales cited for katana being superior to other sword styles.
Myth: The folded steel and partial heat-treating make them much stronger than other swords.
Reality: Folding or otherwise layering blades and differential tempering (heat-treating the edge but not the spine of the blade) are neither uniquely Japanese techniques nor even actually Japanese in origin. Both techniques spread to Japan from China, where they had been developed and were already in steady use. The same techniques either developed independently or were spread via trade routes in many cultures around the world as a method of solving the universal problem of unhardened steel being too soft to hold an edge well and hardened steel is too brittle to make a whole sword from.
Myth: Their blade curvature is perfectly designed for cutting.
Reality: The curvature of each katana blade may vary substantially, depending on the style, time period and maker. Generally, katana are only slightly curved, but more deeply curved examples are known. The curvature is also by no means unique to the katana, as most sword-making cultures around the world have made curved blades of some variety. It is also important to note that the curvature is a trade-off, relinquishing some of the strengths of a straight sword (such as ease of thrusting) for the extra slicing ability granted by the curve.
Myth: The convex or "apple-seed" blade profile allows them to cut deeper than others.
Reality: As with blade curvature, the convex blade profile (judged by looking at the sword point-first) is both a trade-off and by no means unique to Japanese blades. There are three basic blade profiles, each used for differing situations, and each found in blades from all over the world: convex, flat, and concave. Convex blades are generally more effective against armor as they resist damage better as well as cutting deeper as the curvature and extra weight helps the slicing action of the blade, but are somewhat more difficult to actually achieve a cut within the first place, as they are effectively duller than other types. Concave blade profiles are easier to cut with and can be much sharper than others, but are much more prone to breaking and not as easy to slice deeply with. Flat blade profiles are essentially a compromise between these two.
Myth: They are much sharper than other cultures' swords.
Reality: This myth is perpetuated in large part due to the modern sword manufacturers themselves. Since there is generally more demand for katana than other historical swords, it is often easier to find sharp, well-made katana than a similarly high-quality English or Chinese sword, leading to the misinterpretation that duller blades were historically common in these cultures, when in reality sword sharpness was relatively consistent around the world.
Myth: They were produced with better steel.
Reality: Japan has never been home to large, high-quality deposits of iron ore, making the widespread production of steel fit for swords problematic. Japanese smiths were able to compensate for this through careful smelting, but high-quality steel was very expensive. This led to one area in which katana historically truly have excelled: craftsmanship. With little steel to waste and a higher incentive to prevent imperfections that could lead to sword breakage, Japanese swordsmiths historically focused more on perfecting each blade than did smiths in countries where a broken sword could easily be replaced.