Until 1872 when H.M.S, Challenger, a British warship converted for research, made its historic voyage, relatively little was known about the oceans. The voyage, funded by the British government, was mandated to chart the depth of the ocean, measure the various ocean currents, amass data on the composition of the ocean's water and bottom sediments, and collect information on ocean life. At the time of the voyage, except for a few soundings, almost nothing was known about the ocean bottom. Most scientists of the day had considered the vast expanses of the deep ocean basins to be nothing more than flat, featureless surfaces that, except for a few isolated volcanic islands, extending from one continent to another. The discovery of a submarine mountain range by H.M.S. Challenger was the first indication that the topography of the ocean bottom was not so simple. It is interesting to note that what H.M.S. Challenger had discovered was a portion of the Atlantic mid-oceanic ridge. It would be nearly a century before the oceanic ridges were rediscovered using sonar, an invention of the U.S. Navy, that allowed scientists their first real view of the topography of the ocean basins. Although the data amassed by H.M.S. Challenger significantly expanded our understanding of the ocean, knowledge of the ocean was to remain very limited until the mid 1900s.
Renton, John J. and Repine, Thomas, "Oceans and Shorelines" (2016). Readings and Notes. 24.