CTBTO’s Data and Analysis Pertaining to the Search for the Missing Argentine Submarine ARA San Juan

The Argentine submarine ARA (Armada de la República Argentina) San Juan went missing on November 15th, 2017, with its last confirmed contact location around 600 kilometres East of Comodoro Rivadavia, Chubut, Argentina. In the days following the initiation of the multi-national search and rescue mission, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) analysed data recorded by its International Monitoring System (IMS) sensor network for any signals that could support this effort. Two of the IMS hydrophone stations, HA10 in the central Atlantic Ocean and HA04 in the southern Indian Ocean, were found to have recorded an unusual hydroacoustic signal of unknown nature (a “hydroacoustic anomaly”), which originated from the vicinity of the last known location of the ARA San Juan. On December 1st, 2017, confirmation of the detection and localization capability of the IMS network was made possible by a calibration test involving a depth charge deployed by the Argentine Navy. Also this signal was detected by the two IMS hydrophone stations and its origin located to within 39 km of the announced deployment location. After extended search operations, on November 17th, 2018, the ARA San Juan was found on the seabed at approximately 900 metres depth less than 20 km from the location of the hydroacoustic anomaly provided by CTBTO. This paper presents the methodologies applied by CTBTO within months after the loss of the submarine, aimed at detecting, locating and characterizing the November 15th signal of unknown origin and the December 1st calibration explosion.