French-Epstein Device

The French-Epstein Device is an item in System Shock 2. It can modify any weapon (except one that has already been fully modified) regardless of soldier's Modify skill. It is very rare and is exhausted after a single use. It does not use any Nanites.

Background
F-ED uses Nanites to analyze and modify any weapon, according to its description. In reality, however, the weapon is modified free of charge.

In-Game Strategies
The French-Epstein Device is one of the most valuable tools in the game, due to both its rarity and function. Each Modification to a weapon guarantees a 15% damage bonus (with the exception of first Grenade Launcher Modification that actually doubles damage of all but Disruption Grenades), along with a statistical bonus that is unique to each weapon. Only weapons already modified twice and melee weapons cannot be upgraded.

There are enough French-Epstein Devices in the game to fully modify three weapons on Easy, Normal and Hard difficulties (actually, three and a half on Easy or Normal), except on Impossible difficulty where only 5 F-EDs are found. It's simple to waste them being careless and not having neither Maintenance nor Repair skills (nor using unbreakable weapons). Being careful though, it is possible to max out chosen weapons without putting any points into Modify skill.

Engineering Deck

 * Cargo Bay 2B east side, 3rd level, on Constance Sanger's corpse.

Hydroponics Deck

 * Sector D, room opposite the Replicator in a Security Crate (not present on Impossible difficulty).

Operations Deck

 * East Crew Quarters (lower level), northern room on the west wall, in a Security Crate.
 * Power Ops, in front of Simulation Unit 3 (not present on Hard and Impossible difficulties).

Command Deck

 * Sector B, southernmost Escape Pod area, lying on the ground near a waste container.
 * Sector A Shuttle Control, opposite Shuttle Bay 2's functional shield control computer, on left windowsill.

UNN Rickenbacker

 * Deck A, from the Chemical Store Room, follow the first Nacelle B floor sign, go straight at the intersection and follow the corridor to a small room with a Black Egg. The device is lying on the floor there.