Which British expedition first located the depression later called Challenger Deep?

The Challenger expedition was the first British expedition to locate the depression later called Challenger Deep.

The expedition was a pioneering Royal Navy scientific voyage that circumnavigated the globe from 1872 to 1876 aboard HMS Challenger. On 23 March 1875, the ship took soundings at station 225 in the western Pacific, between Guam and Palau. Its crew recorded a depth of 4,475 fathoms—then the deepest sounding obtained during the voyage.

The original measurement was made with a weighted line rather than modern sonar, and the ship’s position was determined by celestial navigation. Even so, the sounding identified the area as an extraordinary depression at the southern end of what is now called the Mariana Trench. Later surveys found much greater depths nearby and established the feature’s record-setting status.

A common mix-up is confusing the expedition that first located the depression with later missions that measured it more accurately. HMS Challenger II surveyed the area in the early 1950s, while the bathyscaphe Trieste made the first crewed descent in 1960. The name commemorates both Challenger vessels.