How do you find the deepest part of the sea?

The first depth measurements in the Mariana Trench were made by the British survey ship HMS Challenger, which was used by the Royal Navy in 1875 to conduct research in the trench. The greatest depth that they recorded at that time was 8,184 meters (26,850 feet).

In 1951, another Royal Navy vessel, also named the "HMS Challenger," returned to the area for additional measurements. They discovered an even deeper location with a depth of 10,900 meters (35,760 feet) determined by echo sounding. The Challenger Deep was named after the Royal Navy vessel that made these measurements.

In 2009, sonar mapping done by researchers aboard the RV Kilo Moana, operated by the University of Hawaii, determined the depth to be 10,971 meters (35,994 feet) with a potential error of ± 22 meters. The most recent measurement, done in 2010, is the 10,994 meter (± 40 meter accuracy) depth reported at the top of this article, measured by the United States Center for Coastal & Ocean Mapping.