The japanese katana sword is the favored weapon of the Samurai class of ancient Japan. Its evolution as a cutting weapon occurred over many centuries, during which its size increased along with its complexity and elegance. In 1934 the Japanese government issued a military specification for the shin gunto (new army sword), the first version of which was the katana. Many hand- and machine-crafted swords used by the Japanese army during World War II conformed to this and later shin gunto specifications.
The katana is produced using the tatara-buki method, an original technique that does not depend upon iron ore imported from other countries. It utilizes black iron sand found on the beaches of Japan and achieves fast reduction at low temperature. This creates steel known as Tamahagane, which is very hard and has a razor sharp edge. The swordsmith’s skill is evident in the hammering process as the blade is heated and shaped, giving it a distinctive upward curve. The smith also creates the ridge line, or shinogi, that separates the back (mune) and the thinner edge of the blade from the tang.
A short sword called wakizashi is a general term for a sword between one and two shaku long. It was carried in the scabbard of a katana or tachi as a close-combat and auxiliary sword. It was also used in close combat when fighting from horseback, but it was less effective for slashing at an opponent than the katana. More information here