There is a growing literature on variations of military masculinities in armed groups which focuses mainly, but not exclusively, on Leftist guerrilla groups. Although these empirical studies deal with military masculinities in highly ideologized contexts, it remains theoretically and conceptually unclear how exactly ideology and masculinity constructions are interrelated. Drawing inspiration from civil war literature, I make the theoretical argument that ideology matters in the form of the military masculinity an armed group seeks to construct. I build on the concept of hegemonic masculinity, highlighting its practice-theoretical implications of which the notion of background knowledge is of particular interest. Here, I locate configurations of masculinity as well as ideology. Conceptualizing armed groups as total institutions, ideology, first, shapes the form of the institution and, secondly, is itself conveyed to combatants via socializing practices. It is via these same socialization processes that not only masculinities are carefully constructed but that these gender constructions are thoroughly shaped by ideological thought. My theoretical argument allows for a more nuanced explanation of ideology and military masculinities and, thus, further adds to broader Feminist debates about their variation. At the end, I illustrate the added value of my theoretical argument with empirical notes on the Salvadoran Frente Farabundo Martí de la Liberación Nacional (FMLN).