The advance of the French armies and those of Muenster and Cologne to attack the eastern frontier of the United Provinces met with little serious resistance. Fortress after fortress fell; the line of the Yssel was abandoned. Soon the whole of Gelderland, Overyssel, Drente and Utrecht were in the possession of the enemy. Even the castle of Muiden, but ten miles from Amsterdam, was only saved from capture at the last moment by Joan Maurice throwing himself with a small force within the walls. The Prince of Orange had no alternative but to fall back behind the famous waterline of Holland. He had at his disposal, after leaving garrisons in the fortresses, barely 4000 men as a field-force. With some difficulty the people were persuaded to allow the dykes to be cut, as in the height of the struggle against Spain, and the country to be submerged. Once more behind this expanse of flood, stretching like a gigantic moat from Muiden on the Zuyder Zee to Gorkum on the Maas, Holland alone remained as the last refuge of national resistance to an overwhelming foe. True the islands of Zeeland and Friesland were yet untouched by invasion, but had Holland succumbed to the French armies their resistance would have availed little. At the end of June the aspect of affairs looked very black, and despite the courageous attitude of the young captain-general, and the ceaseless energy with which the council-pensionary worked for the equipment of an adequate fleet, and the provision of ways and means and stores, there seemed to be no ray of hope. Men's hearts failed them for fear, and a panic of despair filled the land.

Had the combined fleets of England and France been able at this moment to obtain a victory at sea and to land an army on the coast, it is indeed difficult to see how utter and complete disaster could have been avoided. Fortunately, however, this was averted. It had been De Witt's hope that De Ruyter might have been able to have struck a blow at the English ships in the Thames and the Medway before they had time to put to sea and effect a junction with the French. But the Zeeland contingent was late and it was the middle of May before the famous admiral, accompanied as in 1667 by Cornelis de Witt as the representative of the States-General, sailed at the head of seventy-five ships in search of the Anglo-French fleet. After delays through contrary winds the encounter took place in Southwold Bay on June 7. The Duke of York was the English admiral-in-chief, D'Estrees the French commander, and they had a united force of ninety ships. The Dutch, who had the wind-gauge, found the hostile squadrons separated from one another. De Ruyter at once took advantage of this. He ordered Vice-Admiral Banckers with the Zeeland squadron to contain the French, while he himself with the rest of his force bore down upon the Duke of York. The battle was contested with the utmost courage and obstinacy on both sides and the losses were heavy. The advantage, however, remained with the Dutch. The English flag-ship, the Royal James, was burnt; and the duke was afterwards three times compelled to shift his flag. Both fleets returned to the home ports to refit; and during the rest of the summer and early autumn no further attack was made on De Ruyter, who with some sixty vessels kept watch and ward along the coasts of Holland and Zeeland. The Dutch admiral had gained his object and no landing was ever attempted.