In 1866, he became captain of the Hawaii-registered ship W.C. Talbot and undertook trading trips through the Bering and Chukchi Seas to locations in Alaska and Chukotka.
[1][2] From 1872 to 1874, when whales became more of a rarity in Arctic waters, Dallmann was commissioned to explore the Antarctic seas on the sailing-steamer Grönland.
The operation was moderately successful from a whaling point-of-view, but more importantly, Dallmann made many discoveries around Antarctica—among others the Bismarck Strait.
Between 1877 and 1884, on behalf of Russian financier Baron von Knoop, Dallmann made annual attempts to haul freight to the Gulf of Ob and the Yenisei Gulf, to be exchanged for grain and other cargoes brought down the great Siberian rivers by means of barges.
Despite the few failures, Dallmann had received the rare opportunity to explore many of the Kara Sea-islands and shores seen by few Europeans.