GURPS Traveller: Star Mercs (1999)

From Back Cover:

Prepare for War . . . with Star Mercs. Everything you need for a star-spanning, military-oriented campaign in the Traveller universe is here!

• Experience combat (and a soldier's life) in the 57th century;
• Learn how to recruit, organize, and equip a mercenary unit;
• Familiarize yourself with the Imperial rules of war;
• Get the edge with discourses on strategy and tactics;
• Arm your troops from a comprehensive list of weapons and other tools of the soldier's trade.

Star Mercs also includes deck plans for the 800-ton Broadsword-class mercenary cruiser, templates for military and mercenary soldier characters, sample missions, and a variety of units and NPC personalities your mercenary group might encounter, including the famed and feared Imperial Marines.