VR Missions
From the Metal Gear Wiki
VR Missions were a group of levels designed to help train rookie agents in the way of combat, stealth, etc etc. The missions took place in a Virtual Reality environment, so not only did it guarantee safety, but the programs could be edited to produce almost any situation possible, so the missions could range from simple combat training to taking down giant guards or enemy UFO's.
The missions were frequently divided into three modes: sneaking mode, weapons mode and alternative mode.
Raiden underwent extensive VR Training before infilrating Big Shell.
