In anti-submarine warfare, how do active and passive sonar differ in terms of detection range and stealth?

• A. Active sonar emits pulses to detect targets but reveals own position; passive sonar listens for noises for stealth but cannot determine range as precisely without corroboration.
• B. Passive sonar emits pulses to detect targets but reveals own position.
• C. Active sonar uses passive listening and does not reveal position.
• D. Passive sonar detects targets only when they are in visual range.

Answer: (A)

Active sonar and passive sonar sit on opposite ends of the detection-versus-stealth trade-off in anti-submarine warfare. When you use active sonar, you emit a sound pulse and listen for echoes off targets. That time-of-flight and the pattern of echoes let you determine range and bearing with relatively good accuracy, giving you a longer detection range. But sending out a pulse makes your own submarine loud and easy to detect, revealing your position to any nearby adversaries and potentially exposing you to counter-detection or countermeasures.

With passive sonar, you’re only listening for sounds produced by others—engine noise, propeller cavitation, machinery, torpedo wakes, and natural sounds in the ocean. This approach is much stealthier because you’re not transmitting, so you’re far harder to detect. However, without active emissions you don’t directly know how far away the sound-source is; bearing can be estimated with an array, but precise range determination requires corroboration from multiple sensors, methods, or additional data. So, passive offers stealth with uncertain or less precise range information, while active provides exact range (and bearing) at the cost of giving away your own position.