The Commonwealth began to prepare for war, but as both nations were unready, war might have been delayed if not for an unfortunate encounter between the fleets of Dutch Lieutenant-Admiral Maarten Tromp and General at Sea Robert Blake in the English Channel near Dover on 29 May 1652. An ordinance of Cromwell required all foreign fleets in the North Sea or the Channel to dip their flag in salute, reviving an ancient right the English had long insisted on. Tromp himself was fully aware of the need to give this mark of courtesy, but partly through a misunderstanding and partly out of resentment among the seamen, it was not given promptly, and Blake opened fire, starting the brief Battle of Dover. Tromp lost two ships but escorted his convoy to safety.