NRP Almirante Gago Coutinho (A523) is a ship of the Portuguese Navy' Dom Carlos I-class survey vessels (ex-US adapted in Portugal for the execution of hydrography and oceanography surveys). Before transfer to the Portuguese Navy, Almirante Gago Coutinho was formerly USNS Assurance (T-AGOS-5) of the United States Navy.
The s were succeeded by the longer . Assurance had an overall length of and a length of at its waterline. It had a beam of and a draft of . The surveillance ship had a displacement of at light load and at full load. It was powered by a diesel-electric system of four Caterpillar D-398 diesel-powered generators and two General Electric electric motors. This produced a total of that drove two shafts. It had a gross register tonnage of 1,584 tons and a deadweight tonnage of 786 tons.
The Stalwart-class ocean surveillance ships had maximum speeds of . They were built to be fitted with the Surveillance Towed Array Sensor System (SURTASS) system. The ship had an endurance of thirty days. It had a range of and a speed of . Its complement was between thirty-two and forty-seven. Its hull design was similar to that of the s.
USNS Assurance was a Stalwart-class modified tactical auxiliary general ocean surveillance ship of the United States Navy. Stalwart-class ships were originally designed to collect underwater acoustical data in support of Cold War anti-submarine warfare operations in the 1980s.
In 1999, ex-USNS Assurance was transferred to Portugal and is now NRP Almirante Gago Coutinho survey ship.