This is a term used by the military to refer to anything that augments a soldier's ability to wage war. Usually an advance in technology, a force multiplier is not limited to a bigger weapon, but can also include improvements in weapons, tactics, and basic equipment that increase the power of an individual soldier to bring the fight to the enemy.

Here are some famous examples:

More recent force multipliers include the laser rangefinder and the laser designator (hell, anything involving lasers), smart bombs, computers, night vision, kevlar, and better uniform designs. Just about any technological advance is reflected in new equipment that better enables a soldier to operate. When it does, it is called a force multiplier.