Originally Posted by
Octane
No, that's why I asked the question...
Put simply, dead submarines don't make any noise, and they tend to sit on the seabed, both of which make them hard to spot.
They'll probably locate it using side-scan sonar, but that takes time to set up, and at this stage there seems little need for urgency.
Edit: The other point is that if you're still hoping to rescue people, you're going to focus your efforts on looking for a live submarine, even if that decreases the chance of finding a dead one.