Throughout the early part of the war English coastal areas were harassed by French raids. The port towns of Portsmouth, Southampton, Hastings and Plymouth were captured and razed, as were many smaller places. Numerous English merchant ships, and several warships, were captured. In June 1340 Edward III smashed the French fleet at the Battle of Sluys. In 1346 the English landed in northern Normandy and undertook a devastating chevauchée through northern France. The English navy paralleled the march of the army, capturing or burning large numbers of French warships and merchant vessels as it went. Thereafter the threat from the French navy was much reduced. The English then soundly beat the French at the Battle of Crécy and captured the major French port city of Calais. The Truce of Calais was agreed in September 1347 but the war continued via raids and guerrilla warfare; the ongoing fighting was "almost constant".