Excerpts from Books and Wikipedia
"The Battle of Sluys, also called Battle of l'Ecluse, was a sea battle fought on 24 June 1340 as one of the opening conflicts of the Hundred Years' War between England and France. The encounter happened during the reigns of Philip VI of France and Edward III of England, in front of the town of Newmarket or Sluis (French Écluse), on the inlet between West Flanders and Zeeland. During the battle Philip's navy was almost completely destroyed, giving the English fleet complete mastery over the channel. However, by the end of Edward's reign the French had rebuilt their fleet and were to become a threat again." [Wikipedia] "The defeat at Sluys dealt a heavy blow to French pretensions to exercise any control over the seas." [Cambridge Illustrated History of Warfare, p. 101]