What else would you expect?
The Rocket Launcher is exactly what it sounds like. This weapon boasts the ability to shoot rockets, which acted like Bombs when they hit an enemy or surface. These rocket projectiles will travel in a straight line away from the player and are not affected by any sort of gravity/bullet drop. It should be noted that the rockets themselves do a substantial amount of damage; however, the fire rate of the weapon is rather slow. Moreover, fire rate upgrades seem to have only a small effect on this weapon.
Most importantly, the Rocket Launcher uses normal stat upgrades in its computations of damage, fire rate, etc. This mean picking up Blow Fish will grant the user poison damage while the acquisition of Poison Bombs will not affect the weapon. In addition, this also means the weapons damage can be increased more than once from items such as Rum and Kiss of Death.