bill of health: a certificate saying that a departing ship's company is healthy (to be presented at the next port of arrival)
certificate: a document attesting to the truth of certain stated facts
vx gas: a highly lethal nerve agent used in chemical warfare; a toxic liquid that penetrates the skin or lungs to disrupt the nervous system and stop respiration; in combat VX gas is deployed by detonating a container over the target area and can persist in the environment up to several weeks after release