Short blade

The Short Blade is a short, curved blade that is a smaller, more agile weapon than the longsword. The Short Blade trades power and reach for a faster swing rate. The Animus, in its hints and tips given to the player, recommends the Short Blade for killing off large numbers of enemies.

Assassin's Creed
In Assassin's Creed, the short blade is first available after Altaïr has reached level 3. Like the Longsword, Altaïr's Short Blade increases in quality and power with his rank. Altair carries the short blade on his back with the handle facing down.

While the Short Blade is selected, the player can also use throwing knives by holding down the modifier key and pressing the weapon hand key ( on Playstation 3, X on Xbox 360, Left Mouse Button for PC default layout).

Assassin's Creed II
Ezio can carry a short blade in addition to his longsword. Various short blades can be purchased at blacksmith shops with unique speed, damage and deflection properties. Unlike Altaïr, he won't carry it on his back, but next to his longsword. The special attack of most short blades can only be preformed from behind, and takes the form of slitting their neck, and stabbing them in the shoulder or the back, which will always result in an instant kill.