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With the Silent Running perk, running no longer factors into a successful sneak attempt.— In-game description

Silent Running is a perk in Fallout 3.


This perk drastically increases the ability to crouch-run through buildings to achieve Sneak Attack Criticals. Together with the Chinese stealth armor, the player character is virtually invisible to non-player characters, even when using the Pip-Boy 3000's light.


  • Silent Running completely negates all movement penalties, regardless of movement speed. The detection level for the player character is the same when standing still or moving around, no matter if moving slowly or running. Without this perk, the movement penalty for moving slowly is 10% and 20% for running. Detection is measured based on a scale of -100 to 0. At -100, the player character is undetectable. At -20%, enemies will enter [CAUTION] mode and start searching. When the detection level reaches a positive number, one will be detected. Without Silent Running, an enemy who doesn't detect the player character (at detection level -30) will immediately enter [CAUTION] mode if one runs towards him, as the penalty will increase the detection level from -30 to -10 right inside the critical stage. With the Silent Running perk, one can move closer and the enemy will not detect them as long as the detection level stays below -21. The player character's speed doesn't matter, since there is no penalty for movement with this perk. Whether moving slowly or running, it will equate to standing still. The numbers above apply to enemy Perception based on sight. Sound-based perception is affected as well with high Sneak, regardless of footstep sound generated.
  • With this perk, 100 Sneak and a cloaking field (with Stealth Boy and/or Chinese stealth armor in Fallout 3), the only way to be detected is by shooting enemies with a loud weapon repeatedly, or by walking into them.
  • Despite being labeled as "silent" running, one still generates the same amount of noise from their footsteps as usual, but non-player characters don't react to it.

Behind the scenes

The perk is a reference to the 1972 film Silent Running, which was set against a post-apocalyptic sci-fi backdrop.