On December 3, 1979, Macheteros gunmen ambushed a U.S. Navy bus carrying personnel to the Sabana Seca communications station, killing two sailors and wounding ten. Communiqués claimed the attack jointly with other armed groups as retaliation for the death of Ángel Rodríguez Cristóbal — the Vieques protester found hanged in his cell at the federal prison in Tallahassee a month earlier, a death the movement regarded as murder — and for the 1978 police killings of two young independentistas at Cerro Maravilla.
Sabana Seca was the deadliest single action of the island's armed struggle and marked the Macheteros as the FBI's chief target in Puerto Rico. No one was ever convicted for the ambush itself; its cited grievances — Vieques, Cerro Maravilla, deaths in custody — remained the movement's central political indictments of the United States.