two discuss their friend Carl, who had been killed earlier in the war. Rico is commissioned a temporary third lieutenant for his final test: a posting to a combat unit. Under the tutelage of his company commander, Captain Blackstone, and with the aid of his platoon sergeant, his boot camp drill instructor Fleet Sergeant Zim, who was reassigned from Mobile Infantry boot camp, Rico commands a platoon during "Operation Royalty", a raid to capture members of the Arachnid brain caste and queens. Rico then returns to the officer school to graduate. The novel ends with him holding the rank of Second Lieutenant, in command of his old platoon in the Rodger Young, with his father as his platoon sergeant. The platoon has been renamed "Rico's Roughnecks", and is about to participate in an attack on Klendathu. Major themes Commentators have written that Starship Troopers is not driven by its plot, though it contains scenes of military combat. Instead, much of the novel is given over to a discussion of ideas. In particular, the discussion of political views is a recurring feature of what scholar Jeffrey Cass described as an "ideologically intense" book. A 1997 review in Salon categorized it as a "philosophical novel". Critics have debated to what extent the novel promotes Heinlein's own political views. Some contend that the novel maintains a sense of irony that allows readers to draw their own conclusions; others argue that Heinlein is sermonizing throughout the book, and that its purpose is to expound Heinlein's militaristic philosophy. Militarism Starship Troopers has been identified as being a part of a tradition in US science fiction that assumes that violent conflict and the militarization of society are inevitable and necessary. Although the Mobile Infantry, the unit to which Rico is assigned, is seen as a lowly post by the characters in the story, the novel itself suggests that it is the heart of the army and the most honorable unit in it. In a commentary written in 1980, Heinlein agreed that Starship Troopers "glorifies the military ... Specifically the P.B.I., the Poor Bloody Infantry, the mudfoot who places his frail body between his loved home and the war's desolation—but is rarely appreciated... he has the toughest job of all and should be honored." The story is based on the social Darwinist idea of society as a struggle for survival based on military strength. It suggests that