Katana

The Katana (sometimes also incorrectly called the Hayabusa sword) is a special Armor Permutation unlockable by earning achievements 49 out of 79 Achievements. It is also unlockable by earning the Sandbox Skull, Assembly Skull, and Orbital Skull.

Description
The Katana closely resembles Ryu Hayabusa's Dragon Sword, and is not usable by the player. It is NOT possible to obtain the Katana by gaining 1000 gamerscore. In some cases after the 1.1 update to Halo 3 some people have been able to unlock the Katana by passing the 1000G mark.(i.e. 990 and then unlocking the new "Double Double" achievement for an end result of 1015 will unlock the Katana).

The Katana can no longer be unlocked by just earning 1000G in Halo 3, and it never had been. One of the only ways to unlock the Katana after the 1.2 update and 1.3 is to unlock 49 out of the 79 achievements.

Unlocking 40 of the 79 achievements worth 1000G, the conclusion is that you MUST have 49 achievements to unlock the Katana. For anyone wondering about the achievements and their order it is as listed below for proof of concept.

Listed First to Last in the order they were unlocked:

Though now it seems that the order does not matter, as finding the Sandbox Skull, Orbital Skull, and Assembly skull also unlocks the Katana.

Characteristics
The Katana consists of a normal Hayabusa body with a Katana sword affixed to the back with a white attachment, possibly magnetized. The sheath of the Katana is grey and the handle is a reddish brown color. It is not possible to use this item during gameplay.

Disadvantages
Users have reported that like the Security Shoulders, the Katana can re-lock and unlock again. For example, having 980 gamerscore and obtaining an achievement worth 25 gamerscore may unlock them, but they can later re-lock themselves, requiring the player to obtain more achievements in order to unlock it again.

The way the Katana sticks up can reveal you if you are sniping however if it is shot you do not take damage. It also cannot be stuck by a grenade.

Trivia

 * The Katana is a traditional Japanese sword.
 * There seem to be some markings on the hilt of the sword resembling Japanese characters.
 * The Katana resembles the first Dragon Sword Ryu gets in Ninja Gaiden.
 * The Katana and the Security armor permutations both come with getting 1000 GS/49 Achievements in Halo 3. Because of this, some fans thought that the Katana should have gone with the Security armor instead of the Hayabusa armor.
 * There is a myth that the katana can be stuck with a plasma or spike grenade, this theory has been tested and is not true
 * It is considered by some players to be the hardest armor to unlock, along with the Security helmet, because of the difficulty of some of the game's achievements.
 * There are rumors that a player can be damaged "through" the Katana because it extends out from the player's back (i.e using a plasma grenade or sniping). However, these rumors were proven to be incorrect.
 * The Sword's color cannot be changed, so it is always gray with a red hilt and a white armor attachment.
 * Since the Katana is already slung over the right shoulder, the player equipped with the sword can no longer use this shoulder for weapons. Instead they use the left shoulder. It has also been observed that by slinging a Sniper Rifle over one's shoulder with the Katana, an X is formed.
 * There was recently a glitch discovered by two Halo 3 players, wherein the one received the Katana with only 965 Gamerscore in Halo 3. It seemed to randomly spawn and disappear in the first player's armor selection.
 * Oddly enough, if a player is carrying a back mounted weapon, the gun is slung under the Katana, and where the Katana joins the body, instead of over it. It would seem that it would obstruct the drawing of a weapon, or cause the Katana to fall off, but apparently, it doesn't.
 * The Katana is most popularly viewed with the Hayabusa Helmet and the Rogue Helmet.