In 1669 Schey became extraordinary captain in the Admiralty of Amsterdam. During the Third Anglo-Dutch War, Gilles was captain of the "Tijdverdrijf". In 1674 he joined the squadron of Cornelis Tromp in action against France. In 1675 he was made a full captain. He was captain of the "Essen" at the Battle of Stromboli, and of the "Spieghel" at the Battle of Agosta and the Battle of Palermo. In 1678 he fought under Cornelis Evertsen the Younger. On 6 December 1683 he became Rear-Admiral under William Bastiaensz Schepers during actions in the Baltic Sea.