The modern tools includes several forms of sonar(detection by sound reflection).
Sonar
A device commonly used to locate objects underwater is a sonar system, such as a side-scan sonar or a multibeam sonar. These devices emit sound waves into the water and then receive the echoes bouncing back from objects underwater, creating a detailed image of the seafloor or any objects present.
They use a Sonar system.
The abbreviation SONAR stands for Sound Navigation and Ranging. It is a technique that uses sound waves to detect and locate objects underwater, similar to how bats use echolocation.
an instrument that use echolocation to locate objects
SONAR
Sonar technology uses the reflection of sound waves to detect objects underwater. By emitting sound waves and measuring the time it takes for them to bounce back, sonar systems can create images of underwater environments and locate objects like submarines or fish.
Sonar uses echoes to locate objects by bouncing sound waves off them and detecting the echoes.
Something called echo-location
They use echolocation. They have excellent hearing and eyesight as well.
Submarines use echolocation to detect, locate, and avoid obstacles underwater, as well as to navigate their surroundings. By emitting sound waves and analyzing the echoes that bounce off objects, submarines can map their environment in conditions where visual navigation is limited or impossible.