Philip VI of France () and Edward III of England (), Philip's Great Council in Paris on 24 May 1337 agreed that the Duchy of Aquitaine, effectively Gascony, should be taken back into Philip's hands on the grounds that Edward was in breach of his obligations as a vassal. This marked the start of the Hundred Years' War. Early in 1345, Edward determined to attack France on three fronts: a small force would sail for Brittany; a slightly larger force would proceed to Gascony under the command of the Henry, Earl of Derby; and the main force would accompany him to either northern France or Flanders. The French anticipated, correctly, that the English planned to make their main effort in northern France. Thus, they directed what resources they had to the north, planning to assemble their main army at Arras on 22 July. South-western France and Brittany were encouraged to rely on their own resources. The main English army sailed on 29 June 1345 and anchored off Sluys in Flanders. Edward was unexpectedly threatened with the loss of his Flemish allies, and to avoid this was forced to attend to diplomatic affairs. By 22 July, although the Flemish situation was unresolved, men and horses could be confined on board ship no longer and the fleet sailed, probably intending to land in Normandy. It was scattered by a storm, and individual ships found their way over the following week to various English ports where they disembarked. There was a further week's delay while the King and his council debated what to do, by which time it proved impossible to do anything major with the main English army before winter. Aware of this, Philip VI despatched reinforcements to Brittany and Gascony. During 1345, Derby led a whirlwind campaign through Gascony at the head of an Anglo-Gascon army. He heavily defeated two large French armies at the battles of Bergerac and Auberoche, captured French towns and fortifications in much of Périgord and most of Agenais, and gave the English possessions in Gascony strategic depth. John, Duke of Normandy, the son and heir of Philip VI, was placed in charge of all French forces in south-west France. In March 1346 a French army numbering between 15,000 and 20,000, enormously superior to any force the Anglo-Gascons could field, including all the military officers of the royal household, marched on Gascony. They besieged the strategically and