Answer: (Detailed Solution Below)
Option D: SONAR
Detailed Solution:
The correct answer is “SONAR”.
SONAR (Sound Navigation and Ranging) is specifically designed to detect and locate objects underwater by emitting sound waves and interpreting the echoes that return.
Audiometer: Measures hearing ability.
Galvanometer: Detects and measures small electric currents.
Sextant: Used for measuring angles, primarily for navigation.