USNS Relentless (T-AGOS-18) was a Stalwart-class modified tactical auxiliary general ocean surveillance ship in service in the United States Navy from 1990 to 1993.

[1][2] On the day of her delivery, the U.S. Navy placed the ship in non-commissioned service in the Military Sealift Command as USNS Relentless (T-AGOS-18).

Like the other Stalwart-class ships, she was designed to collect underwater acoustical data in support of Cold War anti-submarine warfare operations against Soviet Navy submarines using Surveillance Towed Array Sensor System (SURTASS) sonar equipment.

She is fitted with modern navigation electronics and oceanographic winches, as well as sophisticated sensors and sampling equipment which her crew and embarked scientists use to monitor the atmospheric and oceanic environment, such as a thermosalinograph, a conductivity-temperature-depth instrument (CTD), a fluorometer, and NOAA's Scientific Computer System.

[5] From her home port at Pascagoula, Mississippi, Gordon Gunter operates throughout the Gulf of Mexico, Atlantic Ocean, and Caribbean Sea.

This mission helped fill a critical data gap in weather information that commercial fishermen, the petroleum industry, and recreational boaters rely upon heavily.