Roemer Vlacq, son of Anna Jansdochter Verrijn and Dirk Vlacq, a physician, apothecary and notary from Gouda, became lieutenant commander of Kits with the Admiralty of Amsterdam in 1671. In 1672, during the Third Anglo-Dutch War, he commanded the frigate Postiljon during the Battle of Solebay under lieutenant admiral Michiel de Ruyter. In 1673 he took part in all battles, commanding the frigate Brak. In 1674 he was commander of the transport vessel Opperdoes during De Ruyter's expedition against Martinique.