From the back of the book:
Soldier's Companion combines the excitement of the 19th-century colonial wars with the adventure of Space: 1889. The basic system mechanics are an elaboration on those used in Sky Galleons of Mars, giving a solid basis for land, aerial, and aquatic combats. At heart, however, Soldier's Companion is a good, solid set of 19th-century colonial miniatures rules. While allowing for the addition of land juggernauts, combat tripods, and aerial flyers, the rules work just as well for a rag-tag British column fighting its way through the passes of the Northwest Frontier.
Book I: "The Rules of War" constitute the miniatures rules.
Book II: "The Road to War" provides brief campaign rules and rules for integrating Soldier's Companion into Space: 1889 role-playing campaigns.
Book III: "The Sinews of War" covers the wealth of military equipment available, including artillery and naval vessels.
Book IV: "Army Lists" provides an extensive listing of all of the major armies of Earth. In addition, the lists detail the colonial and native armies on Mars (including a full British order of battle for the red planet), Venus, and Luna.
Book V: "Charts and Miscellaneous" puts all the games charts in a single spot, along with the designer's notes and bibliography.
Soldier's Companion will prove a valuable resource to players of Space:1889 and to those who wish to recreate campaigns and battles of the 19th century.