Submersibles typically have ports on the outside specifically for an emergency oxygen line.
What oxygen line would function under 6000 pounds of external pressure? It would need to be as stiff and strong as the sub itself. This isn’t 100ft, or 200 ft down, it is 12,500ft.
A port would be a huge safety risk at the pressures this sub is supposed to operate. This sub is a carbon fiber tube bolted shut from the outside. No ports. They could be floating on the surface right now and still suffocate if they aren’t found.
This is not your typical sub.
Reminds me of my neighbor making a blimp in his garage when I was growing up.
Never did fly.
This is not your typical sub nor is it your typical depth.
It has no port.