In anti-submarine warfare, which statement best describes when to use passive sonar versus active sonar?

• A. Use passive when you need precise range; use active to avoid tipping off the submarine
• B. Use passive to listen without revealing presence; use active to obtain range and bearing
• C. Use passive only in open water; use active only near coast
• D. Use passive to jam; use active to interrogate

Answer: (B)

The idea behind this question is how stealth vs information is balanced in sonar use. Passive sonar listens for sounds in the water without emitting anything, so your own presence remains hidden from the submarine. This makes passive ideal for initially detecting and tracking a target while staying unseen. The information you get passively is mainly bearing from where the sound arrives on the hydrophones; range is difficult to determine accurately without emitting a signal.

Active sonar, on the other hand, sends out a ping. The time it takes for the ping to travel to the submarine and return as an echo lets you calculate range, and the echo direction helps you determine bearing. This gives you a precise fix on the target, but the trade-off is that your own sonar emissions can reveal your position to the submarine and potentially to others in the area.

So the statement that passive is used to listen without revealing presence and active is used to obtain range and bearing best captures the respective roles and trade-offs of the two sonar modes.