After a short period of peace Edward, in July, 1336, ravaged and burned Scotland as far as Aberdeen, but growing complications with France compelled him in the same year to return to England. Though he professed to have a claim, through his mother, on the French throne against Philip of Valois, that claim was left in abeyance until several acts of aggression on the part of Philip brought about a rupture between the two kings. The Count of Flanders, at Philip's instigation, had broken off commercial relations with England; French privateers were daily committing ravages on English commerce; Aquitaine was continually threatened by desultory attacks; and Philip, though he hesitated to accept the responsibility of being the first to declare war, scarcely attempted to conceal his endeavors to throw that responsibility on Edward. Edward sailed for Flanders July 16, 1338, and at Coblentz held a conference with the Emperor Louis V., at which the latter appointed him his vicar-general, and gave orders for all the princes of the Low Countries to follow him in war for the space of seven years. In 1339 Edward laid siege to Cambrai, but soon afterward raised the siege and invaded France. Philip advanced to meet him, but declined battle, and Edward concluded his first campaign without achieving anything to compensate him for its cost. In 1340 he defeated the French fleet before Sluys. The French fleet of one hundred and ninety galleys and great barges was superior to his in strength, for many of his ships were small. Nineteen of their ships were the biggest that had ever been seen, and grandest of all was the Christopher that had been taken from the English. Edward's fleet seems to have been "to the leeward and westward" of the enemy, and about noon he ordered his ships to sail on the starboard tack, so as to get the wind which presumably was north-east, and avoid having the sun in the faces of the archers. Then, having made their tack and got the wind, his ships entered the port and engaged just inside it. The French ships seem to have hugged the shore, and could not manoeuvre, for they were lashed together in four lines. All in three of the lines were taken or sunk, the Christopher and other English ships being retaken; the fourth line escaped in the darkness, for the battle lasted into the night. The king's victory was complete, and the naval power of France was destroyed.