the other Baltic ports, as well as Vladivostok, could not operate in winter, hence the push for Russia to establish naval facilities on the Black Sea coast and (eventually) at Murmansk. And even substantial naval forces in the Baltic Sea remained confined by the lack of free access to the Atlantic via the Øresund, just as the Black Sea Fleet could not always rely on passage through the Bosphorus and the Dardanelles. As a result, separate naval groupings developed in relative isolation in the Baltic, the Black Sea, the Russian Far East and the Arctic. Background Under Tsar Mikhail I (Mikhail Fyodorovich Romanov), the first three-masted ships built within Russia were finished in 1636. Danish shipbuilders from Holstein built it in Balakhna according to contemporary European design. The ship was christened Frederick; during its maiden voyage on the Caspian Sea, the ship sailed into a heavy storm and was lost at sea. During the Russo-Swedish War, 1656-1658, Russian forces seized the Swedish fortresses of Dünaburg and Kokenhusen on the Western Dvina. They renamed the former as Borisoglebsk and the latter as Tsarevich-Dmitriyev. A boyar named Afanasy Ordin-Nashchokin founded a shipyard at Tsarevich-Dmitriev fortress and began constructing vessels to sail in the Baltic Sea. In 1661, however, Russia lost this and other captured territories by the Peace of Cardis. Russia agreed to surrender to Sweden all captured territories, and it ordered all vessels constructed at Tsarevich-Dmitriev to be destroyed. Boyar Ordin-Nashchokin turned his attention to the Volga River and Caspian Sea. With the Tsar's approval, the boyar brought Dutch shipbuilding experts to the town of Dedinovo near the confluence of the Oka and Volga rivers. Shipbuilding commenced in the winter of 1667. Within two years, four vessels had been completed: one 22-gun galley, christened Орёл ("Oryol" = "Eagle"), and three smaller ships. Орёл was Russia's first own three-masted, European-designed sailing ship. It was captured in Astrakhan by rebellious Cossacks led by Stepan Razin. The Cossacks ransacked Орёл and abandoned it, half-submerged, in an estuary of the Volga. During much of the 17th century, independent Russian merchants and Cossacks, using koch boats, sailed across the White Sea, exploring the rivers Lena, Kolyma and Indigirka, and founding settlements in the region of the upper Amur. The most celebrated Russian explorer was Semyon Dezhnev who, in 1648, sailed along the entire northern expanse of present-day Russia by way of the Arctic Ocean. Rounding the