Impuzamugambi
According to Human Rights Watch, before April 6, the militias had only about 2,000 members, mostly in Kigali.  However: "Once the genocide began and militia members began reaping the rewards of violence, their numbers [increased quickly] to between twenty and thirty thousand for the [whole] country[.]"  Eventually, the Impuzamugambi and the Interahamwe grew so much that together they had 50,000 members.  That was half as many members as the regular Rwandan Army had.