From the publisher's website:
"There Will Be War!"
"Whether you're trying to stop the Dark Lord's invading army, lead a Ranger company against the Axis in WWII, or command your own crack mercenary regiment in a far-flung star empire, you're likely to get into battles that are far too big to resolve with ordinary GURPS combat. GURPS Mass Combat is the answer! It presents a powerful abstract system that lets you resolve land, sea, and air battles at any tech level. Features include:"
"* Rules for logistics, movement, reconnaissance, and many other things that matter to a military force even when no enemy is in sight."
"* Integral treatment of air superiority, amphibious assaults, airborne troops, sieges, and everything else that's important when the enemy is in sight."
"* Round-by-round resolution that puts the commander in control, letting him choose his strategies and instantly see the results of his skill and cunning."
"* Equal attention to the aftermath of battle: pursuit, casualties, looting, recovering losses, and more."
"Everything is fast and easy to use in play thanks to extensive examples, quick-reference tables, and ready-to-go stats for the strength, weaponry, and mobility of numerous unit types. It's all generic, too, covering realistic, fantastic, and superscience troops at every tech level, and providing guidelines for customizing their quality, special training, and equipment. And it never loses sight of the fact that GURPS is a roleplaying game -- every hero gets a chance to shine, and the rules emphasize what the PCs do and what happens to them."
"GURPS Mass Combat requires only the GURPS Basic Set, Fourth Edition."