Dutch Republic, igniting the Franco-Dutch War. The attack was opposed by the Holy Roman Empire led by Leopold I. In 1674, Sweden was pressured into joining the war by attacking the Republic's northern German allies. France promised to pay Sweden desperately needed war subsidies only on the condition that it moved in force on Brandenburg. A Swedish army of around 22,000 men under Carl Gustaf Wrangel advanced into Brandenburg in December 1674 and suffered a minor tactical defeat at the Battle of Fehrbellin in June 1675. Though not militarily significant, the defeat tarnished the reputation of near-invincibility that Sweden had enjoyed since the Thirty Years' War and emboldened its enemies. By September 1675, Denmark, the Dutch Republic, the Holy Roman Empire and Spain were all joined in war against Sweden and its ally France. Scanian War With the declaration of war against Sweden on 2 September 1675, Denmark saw a chance to regain its recently lost eastern provinces. The southern Baltic became an important strategic theatre for both Denmark and Sweden. Denmark needed the sea lanes to invade Scania, and Sweden needed to reinforce Swedish Pomerania on the Baltic coast; both stood to gain by taking control of the Baltic trade routes. As war broke out between Denmark and Sweden a strong naval presence also became essential for Sweden to secure its interests at home and overseas. In October 1675 the Swedish fleet under Gustaf Otto Stenbock put to sea, but sailed no further than Stora Karlsö off Gotland before it had to turn back to Stockholm after less than two weeks, beset by cold and stormy weather, disease, and the loss of vital equipment. Stenbock, held personally responsible for the failure by King Charles XI, was forced to pay for the campaign out of his own pocket. During the winter of 1675–76 the Swedish fleet was placed under the command of Lorentz Creutz, who attempted to put to sea in January to February 1676, but was iced in by exceptionally cold weather. State of the fleets The First Anglo-Dutch War (1652–54) saw the development of the line of battle, a tactic where ships formed a continuous line to fire broadsides at an enemy. Previously, decisive action in naval engagements had been achieved through boarding and melee, but after the middle of the 17th century tactical doctrine focused more on disabling or sinking an opponent through superior firepower from a