Rocket Launcher Bug
From WikiRaider
The Roket Launcher Bug is one of the useful Bugs. It can be found in Tomb Raider III, the only Classic game that contains the Rocket Launcher. It is especially useful for defeating the Boss enemies in this game.
Using the Rocket Launcher Bug
First, draw the MP5 - any other weapon would work, too, but the MP5 has the highest rate of fire. Then, put the MP5 away again.
Now crouch down and crawl around a bit while holding the key for pulling the weapons - Lara should change to the sitting position.
Finally, stand up and draw the Rocket Launcher by using the shortcut key. If everything has gone right, the Rocket Launcher will fire as fast as the MP5.