Gerard was born in Willemstad, the son of a wood-trader, but chose to enter the Dutch navy in 1661 as a cadet, serving the Admiralty of the Maze. He was made second lieutenant in May 1666 during the Second Anglo-Dutch War. On 10 February 1671 he was promoted lieutenant. During the Third Anglo-Dutch War he served on Michiel de Ruyter's flagship, De Zeven Provinciën, in the Battle of Solebay. He was promoted to extraordinary captain on 15 March 1673, serving as second flagcaptain of De Zeven Provinciën in the Battle of Texel, below captain Pieter de Liefde. On 13 February 1674 he was made a full captain.
