A group of Companions gathered together by force, and which normally functions as a some kind of military unit (> Military Fantasy). Hierarchy is enforced, the top of the triangle normally being occupied by the original recruiter, who may be the agent of an invisible Magus or monarch or Dark Lord. DDs are normally recruited to gain a specific goal, the attainment of which almost certainly involves physical conflict and which exploits the combat skills of the team; fantasy writers, however, tend to equip individual members of the team with a variety of additional Talents. Once its goal has been attained, the team may evolve through mutual appreciation into the Seven Samurai kind of grouping very much more commonly found in fantasy.
The term comes from a nonfantasy novel, The Dirty Dozen (1965) by E M Nathanson (1928-2016), filmed as The Dirty Dozen (1967 US/Spain). [JC]