Directly as the name implies, It is a rocket launcher. The earliest you can come across it in the game is in the third level of the game "Seal the Mines", from which it can be bought from the Barter Droids. However it can be found for free (three drops) in the next level right after, "Clean Up". Firing off a single rocket (with a max load of 3). At level one, the rocket launcher works very universally similar to what you would expect. You fire a single light rocket into an enemy or group of enemies, which deals a moderate amount of damage within a small splash radius. At level two the model is changed, damage increased, and radius doubled. Level three, the weapon is renamed to "Barrage Cannon", and the rocket's damage boosted insanely (Taking away almost to over a full battery of health from Glitch). Above those the most notable difference is that approximately 0.8 seconds after launch, three smaller rockets will split off of the main one, increasing the explosion and direct splash radius damage, truly a walking tank.
Rocket Launcher - Level 1 EditA rather early appearance in the game, the Rocket Launcher first appears in the level "Do Ore Die", the third level of the game. It can be purchased for either 125, 150, or 175 washers from the Barter Droids. (prices vary based on player's current amount of washers.) At level 1 it packs a heavy punch for the beginning segments of the game. On the easier difficulties of the game it can easily kill a Mil Grunt in a single rocket, and dismember and nearly destroy a small group of them (granted they are in close proximity to eachother.)
Ingame description: "Though it has several limitations, the base level rocket launcher is ideal for destroying small groups of Mils"
Rocket Launcher - Level 2 Edit
At level 2, the rocket launcher gains a new model, firing a larger rocket projectile with increased explosion damage and splash radius/damage, and a much faster reload speed. As at level 1 the rocket launcher was a manual-reload, requiring both Mil and droid operators to load a single rocket at a time, which was a heavy drawback to the weapon, the level 2 variant removes this issue with a rotating design that automatically reloads extremely faster. (From about 4 seconds to reloading all three to 1.5-2 seconds.) The upgrade can either be purchased from the Barter Droids or found on the level "Into the Trenches".
Ingame description: "The level 2 rocket launcher removes the single-hand limitations and dishes out more damage."
Barrage Cannon - Level 3 Edit
At level 3 the rocket launcher bears the new name of "Barrage Cannon", which accurately describes the change to it. Upon upgrading the Rocket Launcher to Barrage Cannon status, which increases the splash damage and direct impact damage exponentially. Just over half a second after firing, three smaller rockets will split off from the main rocket fired, which is the source of the damage boost, and splash damage radius. Only a few rockets can take out a fully-charged, shielded Titan.
Ingame description: "One rocket, four times the ass whoopin'. The barrage cannon is a weapon to be reckoned with." Accurately stated.