The Battle of Öland was a naval battle between an allied Danish and Dutch fleet and the Swedish navy in the Baltic Sea, off the east coast of Öland on 1 June 1676. The battle was a part of the Scanian War (1675–1679) fought for supremacy over the southern Baltic. Sweden was in urgent need of reinforcements for its north German possessions; Denmark sought to ferry an army to Scania in southern Sweden to open a front on Swedish soil.
Just as the battle began, the Swedish flagship Kronan sank, taking with it almost the entire crew, including the Admiral of the Realm and commander of the Swedish navy, Lorentz Creutz. The allied force under the leadership of the Dutch admiral Cornelis Tromp took full advantage of the ensuing disorder on the Swedish side. The acting commander after Creutz's sudden demise, Admiral Claes Uggla, was surrounded and his flagship Svärdet battered in a drawn-out artillery duel, then set ablaze by a fire ship. Uggla drowned while escaping the burning ship, and with the loss of a second supreme commander, the rest of the Swedish fleet fled in disorder.
The battle resulted in Danish naval supremacy, which was maintained throughout the rest of the war. The Danish King Christian V was able to ship troops over to the Swedish side of the Sound, and on 29 June a force of 14,500 men landed at Råå, just south of Helsingborg in southernmost Sweden. Scania became the main battleground of the war, culminating with the bloody battles of Lund, Halmstad and Landskrona. Danish and Dutch naval forces were left free to raze Öland and the Swedish east coast all the way up to the Stockholm Archipelago. The Swedish failure at Öland also prompted King Charles XI to order a commission to investigate the fiasco, but in the end no one was found responsible.
In the 1660s, Sweden reached its height as a European great power. It had recently defeated Denmark, one of its main competitors for hegemony in the Baltic, in the Torstenson War (1643–1645) and the Dano-Swedish War (1657–1658). At the Treaties of Brömsebro (1645) and Roskilde (1658), Denmark was forced to cede the islands of Gotland and Ösel, all of its eastern territories on the Scandinavian Peninsula, and parts of Norway. In a third war, from 1658 to 1660, King Charles X of Sweden attempted to finish off Denmark for good. The move was in part due to bold royal ambition, but also a result of Sweden's being a highly militarized society geared for almost constant warfare, a fiscal-military state. Disbanding the Swedish forces meant settling outstanding pay, so there was an underlying incentive to keep hostilities alive and let soldiers live off enemy lands and plunder. In the end, the renewed attack failed with interventions by the leading naval powers of England and the Dutch Republic. Charles' plans to subdue Denmark were thwarted and Trøndelag and Bornholm were returned to Denmark in the Treaty of Copenhagen in 1660 while Sweden was allowed to keep the rest of its recent conquests.
Charles X died in February 1660 and was succeeded by a regency council—led by the queen mother Hedvig Eleonora—that ruled in the name of Charles XI who was only four at the time of his father's death. Sweden had come close to almost complete control over trade in the Baltic, but the war revealed the need to work against the formation of anti-Swedish alliances that included Denmark, especially with France, the most powerful state in Europe at the time. There were some successes in foreign policy with the anti-French 1668 Triple Alliance of England, Sweden, and the Dutch Republic.
While the Swedish policy was to avoid war and to consolidate its gains, Danish policy after 1660 was to seek an opportunity to regain its losses. Under the Oldenburg King Frederick III, the foreign policy was aimed at isolating Sweden while setting itself up in a favorable position in future wars. Denmark attempted to position itself in the alliances among the 17th century Europe great powers. Bourbon France and the Habsburg-dominated Holy Roman Empire competed for continental domination while the Dutch Republic and England fought several wars over naval hegemony. At the same time, Denmark sought to rid itself of the generous toll treaties it was forced to grant Dutch merchants after the Republic's assistance in the wars against Sweden. Attempts were made to ally with both England and France, but without success. In the Second Anglo-Dutch War (1665–1666) Denmark had to side with the Dutch at the Battle of Vågen, souring its relations with England. In 1670 France allied with England against the Republic. Sweden's relations with France had improved greatly and in 1672 it joined the Anglo-French coalition, pushing Denmark into the Dutch camp.
In 1672, French King Louis XIV launched an attack on the 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.
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 1675–1676 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.
The First Anglo-Dutch War (1652–1654) 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 distance. This entailed major changes in military doctrines, shipbuilding, and professionalism in European navies from the 1650s onwards. The line of battle favored very large ships that could hold the line in the face of heavy fire, later known as ships of the line. The new tactics also depended on the ability of strong, centralized governments to maintain large, permanent fleets led by a professional officer corps. The increased power of the state at the expense of individual landowners led to the expansion of armies and navies, and in the late 1660s Sweden embarked on an expansive shipbuilding program.
In 1675, the Swedish fleet was numerically superior to its Danish counterpart (18 ships of the line against 16 and 21 frigates against 11), but it was older and of poorer quality than the Danish fleet, which had replaced a larger proportion of its vessels. The Swedes had problems with routine maintenance, and both rigging and sails were generally in poor condition. Swedish crews lacked the professionalism of Danish and Norwegian sailors, who commonly had valuable experience from service in the Dutch merchant navy, and the Swedish navy also lacked a core of professional officers. The Danish had seasoned veterans like Cort Adeler and Niels Juel. The Danish fleet was also reinforced with Dutch units under the command Philip van Almonde and Cornelis Tromp, the latter an experienced officer who had served under Michiel de Ruyter, famous for his skilled command during the Anglo-Dutch Wars.