Cannon

From Gineipaedia, the Legend of Galactic Heroes wiki

Warships utilize a number of very powerful electron laser cannons that can fire across exceptionally large distances and still maintain a high level of accuracy. These cannons are typically recessed into the hull of the ship, with a movable focusing lens near the end of the barrel that allows the beam to be fired at different angles. (A typical electron laser cannon can be fired, for example, at a 30 degree angle).

Due to powerful electromagnetic-interference (as a result of both ECM and natural stellar phenomena) it is very hard,, to "lock on" to an enemy ship with computer targeting, they can be aimed cannons to be aimed and fired manually. Because of this, most warships are equipped with a large number of these cannons, firing all of them simultaneously in the general direction of an enemy ship, hoping to score a hit.