In 1657 Denmark, with Dutch support, declared war on Sweden as a means of frustrating Charles X's plans for the Swedish domination of the Baltic and its vast hinterland. Quite apart from its fundamental opposition to a Swedish subjugation of Denmark, the Netherlands, with its extensive trading connections throughout Northern Europe, did not want to find itself having to obtain Swedish permission to use The Sound, the only entry into the Baltic Sea and the key to those territories beyond. The War began with an indecisive action between the evenly-matched Danish and Swedish fleets off Falsterbo in September 1657 and this was followed, in February 1658, by the short-lived Peace of Roskilde. Satisfying neither side, Charles X broke the peace and resumed hostilities after five months by sending his fleet under Count Wrangel to blockade Copenhagen, a decision he came to regret as it brought about the active involvement of the Dutch whose fleet was the most powerful in Western Europe. When the Danish request for assistance reached The Hague that summer, the Dutch did not hesitate and, as soon as it could be made ready, their fleet put to sea under the command of Jacob van Wassenaer van Obdam.
This atmospheric work of a great fleet at sea and beating its way through one of Europe's most contested stretches of open water must surely depict the Dutch en route to their celebrated encounter with the Swedes in one of the largest sea battles in Scandinavian history. The Dutch fleet consisted of thirty-five ships-of-the-line, in company with thirty transports containing 2,000 soldiers, whilst the Swedes had the same number of men o'war together with eight smaller armed vessels. As the Swedish fleet waited off Helsingor, the Dutch sailed through The Sound early on the morning of 29th October (1658) and battle was joined at about 8.00am. in the narrow seaway between the Danish island of Zeeland and the southern tip of Sweden. The two flagships, Victoria (Count Wrangel) and Eendracht (Wassenaer), were soon disabled and both fleets suffered extensive damage exacerbated by the fact that they were so well matched. Apart from the Brederode (Tromp's old flagship), the Dutch lost several smaller ships and about 1,700 men, including two admirals, were killed. Swedish losses amounted to only three ships and slightly fewer men but they nevertheless decided to break off the action and withdraw in the late afternoon. Despite this lack of any outright victory, Copenhagen was relieved and the Dutch fleet was left in control of The Sound with Swedish power and influence curtailed for the remainder of the War.