Star Guard is an early science fiction novel by Andre Norton, published in 1955.
In 3956, young Kana Karr is about to go on his first mission as an Arch, or archaic mercenary, one of a company of mercenaries (a "Horde") hired out by Terra to fight on primitive worlds with primitive weapons: small arms, but no motorized equipment. Another class of Terran mercenaries, the Mechs, are employed to fight with mechanized equipment like crawlers and flying wings on more advanced planets of the Galactic civilization. The supplying of Arch and Mech companies is the role to which Terra has been assigned by Central Control. The novel tells of the Horde's difficulties, Kana's maturation both personal and professional, and the ultimate revelation of a surprising secret. The central plot device of the novel--the mercenary companies betrayed and having to fight their way back to safety--follows in some detail Xenophon's description of Greek mercenaries in the Persian Empire known as the March of the Ten Thousand. This reworking of historical battles or campaigns remains a common feature of military science fiction.
Star Guard is unusual for Norton in that the hero has no personal emotional agonies. The story is propelled by Kana's intelligence and his education in the realities of the world, his increasing understanding and decisiveness, as he, along with the Horde, is forced to deal with unpredictable and difficult situations.