In 1647, Juel was enrolled at the
Sorø Academy. In 1652, Juel entered Dutch naval service. He served his naval apprenticeship under Dutch Admiral
Maarten Tromp (1598–1653) and Dutch Admiral
Michiel de Ruyter (1607–1676), taking part in all the major engagements of the
First Anglo-Dutch War, a conflict between
England and the
Dutch Republic. From 1654 to 1656, he attended Admiral Michiel de Ruyter on two trips to the Mediterranean during engagements against North African pirates. During an indisposition at
Amsterdam in 1655–1656, he acquired a thorough knowledge of shipbuilding. In 1656, he returned to Copenhagen and entered Danish service as a naval officer, and in 1657, he was appointed admiral. He served with distinction during the
Dano-Swedish War (1658–60) and took a prominent part in the defense of
Copenhagen against the forces of King
Charles X of Sweden. Juel then won a European reputation, and raised Danish sea-power to unprecedented eminence, by the system of
naval tactics, which consisted of cutting off a part of the enemy's force and concentrating the whole attack on it. He first employed this maneuver at the
Battle of Jasmund off
Rügen (25 May 1676) when he broke through the enemy's line in close column and cut off five of their ships, despite nightfall prevented him from pursuing them. Juel's operations were considerably hampered at this period by the conduct of his auxiliary, Dutch Lieutenant Admiral
Philips van Almonde (1644–1711), who accused the Danish admiral of cowardice. A few days after the battle of Jasmund, Dutch Admiral
Cornelis Tromp (1629–1691) with 17 fresh Danish and Dutch ships of the line, superseded Juel in the supreme command. Juel took a leading part in Cornelis Tromp's great victory off
Battle of Öland (1 June 1676), which enabled the Danes to invade
Scania unopposed. On 1 June 1677, Juel defeated the Swedish admiral
Erik Carlsson Sjöblad (1647–1725) during the
Battle of Møn. On 30 June 1677, he won his greatest victory, in the
Battle of Køge Bay southwest of Copenhagen. With 25 ships of the line and 1267 guns, he routed the Swedish admiral
Henrik Horn (1618–1693) with 36 ships of the line and 1800 guns. For this triumph, the reward of superior seamanship and strategy at an early stage of the engagement, Juel's experienced eye told him that the wind in the course of the day would shift from S.W. to W. and he took risks accordingly; he was made lieutenant admiral general and a privy councilor. This victory, besides permanently crippling the Swedish navy, gave the Danes the self-confidence to become less dependent on their Dutch allies. In 1678,
Cornelis Tromp was discharged by King
Christian V, who gave the supreme command to Juel. In spring 1678, Juel put to sea with 84 ships carrying 2,400 cannon, but as the Swedes were no longer had the naval strength to engage such a formidable fleet on the open sea, his operations were limited to blockading the Swedish ports and transporting troops to
Rügen. After the
Treaty of Lund in 1679, Juel showed himself an administrator and reformer of the first order, and under his energetic supervision the Danish navy ultimately reached imposing dimensions, especially after Juel became chief of the admiralty in 1683. ==Personal life==