French naval co-operation against England was also promised; and war was actually declared by Louis XIV in the early spring of 1666.  The real cause of this strong action was due to other motives than enmity to England.  The death of Philip IV of Spain in September, 1665, had brought nearer the prospect of there being no heir-male to the vast Spanish monarchy.  The French Queen, Maria Theresa, was the eldest child of Philip; and, though on her marriage she had renounced her claim to the Spanish throne, it was well known that Louis intended to insist upon her rights, particularly in regard to the Spanish Netherlands.  He was afraid that the States, always suspicious of his ambitious projects, might be tempted to come to terms with England on the basis of a defensive alliance against French aggression in Flanders and Brabant, for both powers were averse to seeing Antwerp in French hands.  To avert this danger Louis determined to take part in the war on the side of the Dutch.  The move however was diplomatic rather than serious, for the French admiral, de Beaufort, never sailed into the North Sea or effected a junction with the Dutch fleet.  Nevertheless, as will be seen, his presence in the Atlantic exercised an important effect upon the naval campaign of 1666.

The English fleet was not ready until the beginning of June.  The ravages of the plague and financial difficulties had caused delay; and the fleet only numbered about eighty sail, including a squadron which had been recalled from the Mediterranean.  The “Generals-at-Sea,” as they were called, were Monk and Rupert.  They began by committing the great blunder of dividing their force.  Rupert was detached with twenty ships to keep watch over de Beaufort, a diversion which had serious consequences for the English.  The Dutch fleet, consisting of seventy-two men-of-war with twelve frigates, was the most powerful that the Admiralties had ever sent to sea, not in numbers but in the quality of the ships.  De Witt himself had supervised the preparations and had seen that the equipment was complete in every respect.  De Ruyter was in supreme command and led the van, Cornelis Evertsen the centre, Cornelis Tromp the rear.  On June 11 the English fleet under Monk was sighted between the North Foreland and Dunkirk, and the famous Four Days’ Battle was begun.  The English had only fifty-four ships, but having the weather gauge Monk attacked Tromp’s squadron with his whole force; nor was it till later in the day that De Ruyter and Evertsen were able to come to the relief of their colleague.  Night put an end to an indecisive contest, in which both sides lost heavily.  The next day Monk renewed the attack, at first with some success; but, De Ruyter having received a reinforcement of sixteen ships, the weight of numbers told and Monk was forced to retreat.  On the third morning De Ruyter pursued his advantage, but the English admiral conducted his retirement in a most masterly manner, his rear squadron covering