• This is unlikely. The sub has multiple (like seven I think) different ways of resurfacing, some of which are purely mechanical and work even with a complete power failure. It could’ve got trapped in a fishing net, but it would still be pinging in that case. There are only really two other scenarios: it’s resurfaced and is bobbing around in the sea (unlikely) or the pressure vessel failed and it was instantly crushed to the size of a tin can.

    Edit: Also, running out of oxygen in a situation like this isn’t horrible. The BBC once did a documentary about the most humane way to execute people and it settled on nitrogen-induced hypoxia. Here’s the part where the presenter (a former British politician) experiences hypoxia: https://vimeo.com/83750163#t=2235s

    • Nitrogen-induced hypoxia is painless, but in a sub like that CO2 might turn out to be a big problem, and that is not painless.

      But yeah, the pressure vessel is (or, probably, was) fiberglass. It’s cheap to use but once it cracks it’ll absolutely shatter – this is why “real” subs tend to use metal – and that’s pretty much what I assume has happened. Either that or they’ve been bobbing on the surface with their air slowly running out, because the hatch can’t be opened from the inside.