Your journey begins with Snake imprisoned. This mission serves as a tutorial for basic movement and stealth. Your primary objective is to escape your cell and find your equipment.
While this mission introduces the recruitment system that defines the experience, it lacks the more streamlined Fulton recovery mechanic later perfected in Metal Gear Solid: Peace Walker.
While the prison escape in Portable Ops focuses on rudimentary recruitment, it mirrors the survival-first philosophy central to the upcoming remake, Metal Gear Solid Delta: Snake Eater.