Anything in deep water is hard to detect. Submarines especially so, because they contain stealth technology to defeat trivial detection. Submarines are stealt

Anything in deep water is hard to detect. Submarines especially so, because they contain stealth technology to defeat trivial detection. Submarines are stealthy. Very stealthy. She likely has magnets to counteract detection by magnetic anomaly detectors (MAD). Many subs also have anechoic tiles to make them less visible to active sonar (but I don't know if this was the case in this instance). If its sank and the crew aren't able to deliberately make a lot of sound then it'll have to be found by sonar sweeps. This survey can be done by the kind of ship that Russia has sent to help find the sub.