In the first six months of 1642, relations between the king and Parliament broke down completely, and factions supporting both sides took up arms. Parliament returned Vane to his post as Treasurer of the Navy, where he used connections to bring significant naval support to the Parliamentary side after Charles attempted to arrest five MPs on charges of high treason in December 1641. In June 1642 Charles rejected the Nineteen Propositions, the last substantive set of demands made by Parliament prior to the outbreak of the First English Civil War. After hostilities began that June with the Siege of Hull, Vane was given a seat on the Committee of Safety, which oversaw Parliamentary military activities.