THE declaration of war in March, 1665, found the Dutch navy, thanks to the prescience and personal care of the council-pensionary, far better prepared for a struggle with the superior resources of its English rival than was the case in 1654. John de Witt, aided by his brother Cornelis, had supplied the lack of an admiral-general by urging the various Admiralty Boards to push on the building of vessels in size, construction and armaments able to contend on equal terms with the English men-of-war. He had, moreover, with his usual industry taken great pains to study the details of admiralty-administration and naval science; and now, in company with the Commissioners of the States-General, he visited all the ports and dockyards and saw that every available ship was got ready for immediate service, provided with seasoned crews, and with ample stores and equipment. The English on their side were equally ready for the encounter. After the death of Cromwell the fleet had been neglected, but during the five years that had passed since the Restoration steps had been taken to bring it to an even greater strength and efficiency than before. Whatever may have been the faults of the Stewart kings, neglect of the navy could not be laid to their charge. One of the first steps of Charles II was to appoint his brother James, Duke of York, to the post of Lord-High-Admiral; and James was unremitting in his attention to his duties, and a most capable naval administrator and leader, while Charles himself never ceased during his reign to take a keen interest in naval matters. In his case, as previously in the case of his father, it was lack of the necessary financial means that alone prevented him from creating an English fleet that would be capable of asserting that "sovereignty in the narrow seas," which was the traditional claim of the English monarchy.

The English were ready before the Dutch, who were hampered in their preparations by having five distinct Boards of Admiralty. The Duke of York put to sea with a fleet of 100 ships at the end of April and, cruising off the coast of Holland, cut off the main Dutch fleet in the Texel from the Zeeland contingent. It was unfortunate for Holland that Michael Adriansz de Ruyter, one of the greatest of seamen, was at this time still in the Mediterranean Obdam, to whom the chief command was given, waited until a storm drove the enemy to their harbours. He then united all the Dutch squadrons and crossing to Southwold Bay found the English fleet ready for battle. After some manoeuvring the action was joined on June 13, and after a bloody fight ended most disastrously for the Dutch. The flag-ships in the course of the struggle became closely engaged, with the result that Obdam's vessel suddenly blew up, while that of the English admiral was seriously damaged and he himself wounded. The Dutch line had already been broken, and the fate of their commander decided the issue. The Dutch in great confusion sought the shelter of their shoals, but their habit of firing at the masts and rigging had so crippled their opponents that a vigorous pursuit was impossible. Nevertheless the English had gained at the first encounter a decided victory. Sixteen Dutch ships were sunk or destroyed, nine captured, and at least 2000 men were killed, including three admirals, and as many more taken prisoners. The English had but one vessel sunk, and their casualties did not amount to more than a third of the Dutch losses. The consternation and anger in Holland was great. Jan Evertsen, the second-in-command, and a number of the captains were tried by court-martial; and the reorganisation of the fleet was entrusted to Cornells Tromp, who, encouraged and aided by the council-pensionary, set himself with great energy to the task.

The English meanwhile were masters of the sea, though administrative shortcomings, defects of victualling and shortage of men prevented them from taking full advantage of their success. Early in August, however, a fleet under the Earl of Sandwich attempted to capture a number of Dutch East Indiamen, who had sailed round the north of Scotland. The East Indiamen took refuge in the neutral port of Bergen. Here Sandwich ventured to attack them but was driven off by the forts. While he was thus engaged in the north the Channel was left free; and De Ruyter with his squadron seized the opportunity to return to home-waters without opposition. His arrival was of the greatest value to the Dutch, and he was with universal approval appointed to succeed Obdam as lieutenant-admiral of Holland, and was given the supreme command on the sea. Tromp, angry at being superseded, was with difficulty induced to serve under the new chief, but he had to yield to the force of public opinion. De Ruyter at once gave proof of his skill by bringing back safely the East Indiamen from Bergen, though a severe storm caused some losses, both to the fleet and the convoy. The damage was however by the energy of De Witt and the admiral quickly repaired; and De Ruyter again sailed out at the beginning of October to seek the English fleet. He cruised in the Channel and off the mouth of the Thames, but no enemy vessels were to be seen; and at the end of the month fresh storms brought the naval campaign of 1665 to a close, on the whole to the advantage of the English.