Metal Gear Solid: Peace Walker is an action-adventure stealth video game and is the third action-based Metal Gear title made specifically for the PSP. The gameplay consists of two primary modes: Mission and Mother Base. Mission are the actual action sequences of the game where the player must infiltrate an enemy territory or fight a boss, whereas Mother Base is an army management. Some changes have been made to the standard Metal Gear formula: the player is now unable to move or shoot while laying down and while pinned to a wall, making Peace Walker the first game since Metal Gear to lack any crawling ability.