Asdic
A standard viewing device used on a submarine is a periscope.
The object used to view the outside from inside the submarine is called a periscope.
DIODE
In Britain, ASDIC.In America SONAR.Different names for the same thing!
A light dependent resistor (LDR) is used for the detection of light.A photodiode is a device that converts light into an electrical current.
Charge- coupled device, used majorly in image detection.
A Laser Detection is used to monitor one's speed. It helps eliminate traffic offenses for individuals as they would insert this device in their vehicle.
Radar : radio detection and ranging .
sonar is a device used underwater for locating submerged objects and for submarine communication by means of sound waves.
A U-boat was a submarine used by Germany in World War 1 and World War 2.
This sounds like it's probably the sonar system of a submarine.
Used for error detection