Coast Guardsmen from the USCGC Sequoia (WLB-215), homeported in Apra Harbor, Guam, retrieve a hydrophone in Challenger Deep near the Federated States of Micronesia, Nov. 3, 2015. The crew of the Sequoia and National Oceanic and Atmospheric Administration scientists deployed the hydrophone in an attempt to listen to ambient sound in the deepest part of the Challenger Deep. (U.S. Coast Guard photo by Petty Officer 3rd Class Dylan Hall/Released)