 In October 1658 however a Dutch relief fleet under Lieutenant-Admiral Jacob van Wassenaer Obdam defeated the Swedish fleet in the Battle of the Sound and lifted the sea blockade so that supplies and an auxiliary army could reach the capital.The Dutch were an ally of Denmark from the Anglo-Dutch Wars and were afraid that Swedish control of the Baltic would ruin their profitable trade in this area.After the Copenhageners had withstood about six months of siege, bombardments and attacks, the Swedes attempted to take the city by a grand assault, as a prolonged siege no longer offered any hope of success, now that the sea lanes had been opened by the Dutch.