From the back of the book:
The Heavy Weapons Handbook finishes what Infantry Weapons of the World started, by rating over 170 rocket launchers, grenade launchers, antitank and antiaircraft missle launchers, towed field, antitank, and antiaircraft guns, grenades, mines and other support weapons for Twilight: 2000. Infantry units armed only with rifles and machineguns are only half equipped, the Heavy Weapons Handbook provides the rest of what you'll need.
Weapons covered range from man-portable missile launchers such as the LRAC F1, the Eryx, and the venerable American bazooka, antitank missles ranging from the aging SS-11 surface-to-surface missle to the FOG-M (Fiber Optic Guided Missle), and towed antiaircraft guns from the Swiss 20mm Oerlikon to the Soviet 130mm AA gun. Antiaircraft missles such as Stinger, Blowpipe, and Mistral are also included. The Heavy Weapons Handbook also includes antipersonnel and antitank mines, and recoilless rifles ranging in size from the US M18A1 57mm to the Soviet B-11 107mm.
Each weapon is illustrated, and each entry contains all the information needed for use in the Twilight: 2000 game system, including full combat statistics, weight, price, and availability ratings for both for the weapon and its ammunition.
The weapons covered in the Heavy Weapons Handbook are usable with Twilight: 2000, but also with Merc: 2000, Cadillacs and Dinosaurs, and Dark Conspiracy.