From what I understand, naval submarines typically have a signaling device called an EPIRB mounted in such a way that it's released automatically if the sub div

From what I understand, naval submarines typically have a signaling device called an EPIRB mounted in such a way that it's released automatically if the sub dives significantly below crush depth and/or if a switch isn't activated on some set interval. Then it pops up on the surface and says "Hi, wreck here." I don't think the former system would have worked here anyway, since the sub is supposed to get very close to the bottom.