The Hassler was the early steamship used in the service of the United States Coast Survey. In 1871-72 the ship sailed on the Hassler Expedition, under Commander Philip Carrigan Johnson, brother of Eastman Johnson. This was the first important scientific expedition sent by the government for marine exploration. The expedition included Professor Louis Agassiz and Mrs. Agassiz; Mrs. Johnson; Dr. Franz Steindachner, ichthyologist; Dr. Thomas Hill, botanist; and Count L. F. de Pourtalès, J. A. Allen, and others.
The steamer left Boston December 4, 1871, and reached San Francisco in August 1872. On the way to St. Thomas surface observations were made. Deep-sea dredging was done at Barbados and along the Brazilian coast. At the Straits of Magellan frequent stops were made, and at particularly interesting places several days were spent, and inland excursions undertaken, especially to examine glaciers. Throughout the route collections were made, with much of this material deposited in the Museum of Comparative Zoology at Harvard University. Some of the zoological results of the expedition were published by Agassiz, Lyman, and Pourtalès.