In Halo 1, some Elites eschewed carrying ranged weapons like plasma rifles or needlers, instead opting for the plasma sword, which was essentially a one-hit-kill weapon. It was first seen in the E3 2000 trailer, where it is used both by Elites and by the Master Chief.

Sadly, in Halo 1 the player was unable to pick up or wield this weapon, which evaporated after being dropped.

In Halo 2 campaign and multiplayer, this weapon can be used. It has a lock-on mode that delivers one-hit kills at close range. It cannot be dual wielded. In campaign mode, it has a battery than expires. In multiplayer it can be used indefinitely.

One may assume that the Master Chief will also be able to use the sword in campaign mode should he come across it, but so far information about most aspects of campaign mode is limited, so this has not been confirmed.

The sword is approximately 3 feet in length and was originally assumed to be purely ceremonial in nature.