We cannot be sure, but Leendert den Haen probably served one of Directors from Zeeland, rather than the Admiralty of Zeeland. He was with De Ruyter's fleet in the summer of 1652 and fought in the Battle of Plymouth on 26 August 1652. He commanded the ship Haes in 't Veld, a ship carrying 30 guns and a crew of 108 men. On 12 August, De Ruyter ordered Captains Bouckhorst, de Haen, and Jan van Nes de Jonge Boer, commanding Aert Janszoon van Nes's ship, the Gelderland, to convoy a merchant ship to the Somme and then to return "as quickly as possible". There was a collision and Leendert de Haen's ship was lying in the Somme with the Gelderland, despite Leendert den Haen's ship not having suffered any damage. He was with De Ruyter's fleet when they joined Witte de With's fleet on 2 October. He likely fought in the Battle of the Kentish Knock. We also know that in 1654, he commanded the small frigate Harder (20 guns), a vessel 100ft long. Sources:
- C. T. Atkinson, Ed., The First Dutch War, Vol. VI, 1930.
- James C. Bender, unpublished manuscript "Dutch Ships 1600-1700", 2005.
- Dr. S.R. Gardiner, Ed., The First Dutch War, Vol.II, 1900.