Sonar, which stands for sound navigation and ranging, is a device used for underwater navigation and detection.
A United States military station in the Arctic tracked the Russian submarine Prometheus off the coast of Norway using sonar. When the sub went down the United States investigated further and thought that its final resting place was near Scotland.
Tony Stark used sonar in his Iron Man Armor and found the actual location of the Prometheus. ("And The Sea Shall Give Up Its Dead")