Peter the Great Bay (PGB) was not known to Europeans for a long time. The first European ship reached PGB in 1852. She was the French corvette Capricieuse commanded by captain G. de Rocquemaurel who was sent by his government for exploring the western coast of the Japan Sea; actually he had described the Posyet Bay only. Later the British HMS Winchester and Barracuda visited PGB in August, 1856. They discovered the Golden Horn Bay, them as Port May, and gave names to many other geographical locations. Large Russian expedition of 7 vessels was sent to Primorye coast under the leadership of N.N. Muravyov-Amursky, the Governor-General of Eastern Siberia, in the summer of 1859. They described thoroughly the entire PGB and changed many (not all) foreign geographical names to Russian ones. Scientific researches in the Japan Sea were started soon by L.I. Schrenk, who summarized the results of Russian observations in two books published in 1869 and 1874. Great success in understanding of oceanographic regime was the work of S.O. Makarov «The «Vitiaz» and the Pacific Ocean» (1894). S. Ogura created in 1927 the general chart of currents in the Japan Sea on the base of Japanese observations in 1900–1911 that was more detailed and comprehensive than the first chart of L.I. Shrenk. Moreover, S. Ogura plotted the water temperature and salinity distribution over the whole Japan Sea for February and August. Oceanographic studies in PGB were made in 1920s by K.A. Gomoyunov, the first professional oceanographer who lived constantly in the Russian Far East; he began from the Amur Bay survey in the summer of 1925. The USSR Hydrographic Office conducted the oceanographic survey in PGB and the Tatar Strait in 1926–1928, with measuring of temperature, salinity, dissolved oxygen content, pH, and water transparency, with the deepest measurements at the depth of 3500 m. In 1932, the Pacific Res. Inst. of Fisheries in Vladivostok together with the State Hydrographic Institute in Leningrad organized the large-scale Pacific expedition that covered all Far-Eastern Seas. In the framework of this expedition, the 5 cruises of RV Rossinante to the Japan Sea headed by N.I. Tarasov explored PGB, too, that allowed to analyze seasonal variations of temperature, salinity, oxygen content, and currents. Oceanographic researches in the Japan Sea became more active in the times of WWII, 4 small research vessels made observations at Primorye coast every month from April to October under general supervision of A.M. Batalin; in total, more than 100 exits to the sea were recorded in 1941–1946. The data collected in those years was the basis for the big atlas of the Japan Sea created under the leadership of A.I. Rumyantsev and published in 1951.