This chapter traces the Weatherman faction’s escalation from SDS organizers to an underground guerrilla force in the U.S., highlighting their preparation for violent revolution and the ideological motivations behind it. Members traveled to Cuba and North Vietnam, received explosives and firearms training, and cultivated a network of foreign contacts—including Cuba, North Vietnam, China, the Soviet Union, and Palestinian organizations—often through intermediaries. Domestically, the Weather Underground Organization (WUO) engaged in bombings, arsons, and other attacks, evolving tactics after deadly accidents and tactical disagreements, while parallel groups like New Mobe coordinated mass protests and engaged selectively with foreign actors. Throughout, the FBI tracked these activities, viewing the combination of revolutionary violence and international ties as a serious counterintelligence threat, though intelligence often remained fragmentary or uncertain.