[HWR_14]

As I understand it, the vessel is not able to surface on its own. At its most buoyant, a small amount of the sub will emerge from the water, and that weight will push it back down, so the vast majority of the sub is underwater. This bobbing, which depending on waves can have a small amount or none of the sub above water at any time, would make them hard to detect but easy to retrieve if they were located.

[ehnto]

Imagine being so close yet still not able to escape the vessel. I don't know what is standard for subs, but it strikes me as particularly terrifying that they have no way to open it from the inside.

[HWR_14]

I think, but based on nothing but news stories about this incident, that's common for very deep sea submersibles. It makes sense, the could opt out of a whole bunch of surface ship concerns and they expect to be launched and retrieved. It also helps simplify the design if you don't have to worry about opening hatches from the inside. That adds complexity and can introduce new failure modes.

[gr8flyer1011]

I'm betting that little potty bucket may be filling up...

[eternityforest]

I don't see why that would make them hard to detect. As long as you're above the waves a few percent of the time you should have no trouble getting a signal out, and if you have an antenna you could probably get GPS too, plus, there's some pretty powerful dyes you could release periodically, LEDs that could be seen easily if it's just a few meters of water....

Seems like it would have to be criminally bad design without any kind of signalling at all, to be near the surface and not found within hours.