The Linear Launcher, which from the name is supposed to be a mass driver (a linear motor), fires a large blue lightning ball like projectile. It is very powerful, capable of vaporizing the mutated Alexia Ashford in a single hit. It does however require time to charge for use, and a slight delay to recharge if the shot misses.
In Darkside Chronicles the linear launcher is given a little bit more background, in which it is explained that it was designed in secret by Alexander Ashford specifically to kill Alexia should she ever mutate and become a threat.
Resident Evil CODE:Veronica
"Anti—B.O.W. Linear Launcher An advanced weapon developed to handle B.O.W.s."
It is also an unlockable weapon in Code: Veronica, it is obtained after beating the Battle Game with A rank with all the characters. It can only be used in Battle Game however.
Resident Evil Survivor 2 Code: Veronica
If the player obtained all the jewels in the Arcade Mode, after defeating the Tyrant in Stage 5, Nemesis T-Type will appear and the Linear Launcher is the only weapon capable of killing him. Chris also uses this weapon in the Dungeon Mode. It has infinite ammo. To unlock him, the player has to fully complete clock tower map. It can also be used by Claire and Steve after Vs. Roach Mode is fully completed.
Resident Evil: The Darkside Chronicles
"This powerful, long-ranged weapon must be charged after each shot."