From The Vault

Perk Silent Death Fallout requirements: Level 18, Agility 10, Sneak 80% ranks: 1 benefit: While Sneaking, if you hit a critter in the back, you will cause double damage using a HtH attack. Fallout 2, Fallout Tactics requirements: Level 18, Agility 10, Sneak 80%, Unarmed 80% ranks: 1 benefit: While Sneaking, if you hit a critter in the back, you will cause double damage using a HtH attack.

Silent Death is a Fallout, Fallout 2 and Fallout Tactics Perk.

While Sneaking, if you hit a critter in the back, you will cause double damage using a HtH attack. Silent Death is that kind of Perk.

• Note: A weaker equivalent of this Perk called "Backstab" appears in Lionheart. It has also been carried over to Fallout 3 in the form of sneak attack criticals, which does not require any perk.