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  Tromp, angry at being superseded, was with difficulty induced to serve under the new chief, but he had to yield to the force of public opinion.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.

Nor were the misfortunes of the Dutch confined to maritime warfare.  Between England and Holland indeed the war was entirely a sea affair, neither of them possessing an army strong enough to land on the enemy’s coast with any hope of success; but the United Provinces were particularly vulnerable on their eastern frontier, and Charles II concluded an alliance with the Bishop of Muenster, who had a grievance against the States on account of a disputed border-territory, the lordship of Borkelo.  Subsidised by England, the bishop accordingly at the head of 18,000 men (September, 1665) overran a considerable part of Drente and Overyssel and laid it waste.  There was at first no organised force to oppose him.  It had been the policy of Holland to cut down the army, and the other provinces were not unwilling to follow her example.  No field-marshal had been appointed to succeed Brederode; there was no army of the Union under a captain-general, but seven small provincial armies without a military head.  Some thousands of fresh troops were now raised and munitions of war collected, but to whom should the chief command be given?  William Frederick was dead (October 31, 1664) and had been succeeded by his youthful son, Henry Casimir, in the Stadholderate of Friesland.  Joan Maurice of Nassau had withdrawn from the Netherlands and was Governor of Cleves in the service of Brandenburg.  He was however persuaded to place himself at the head of the army, though complaining bitterly of the inadequacy of the forces placed at his disposal.  De Witt, however, had not been idle.  He secured the assistance of Brunswick-Lueneburg, and an army of 12,000 Brunswickers under the command of George Frederick von Waldeck attacked Muenster; while a force of 6000 French likewise, under the terms of the treaty of 1662, advanced to the help of the Dutch.  Threatened also by Brandenburg, the bishop was compelled to withdraw his troops for home defence and in April, 1666, was glad to conclude peace with the States.