So let me get this straight, the entire sub is controlled by a cheap bluetooth controller? Setup to bluetooth to the engines outside? In water? Where bluetooth radio won't go very far?!
Am I wrong here - SURELY there is manual hard wired back up control of the sub?
If this is not so...........then wow, the song 'dumb ways to die' springs to mind.....
If it is ONLY a bluetooth controller, controlling the entire thing (again surely not and/or there is professional grade control systems as well?!).........but if it is, then my theory is, the sub is perfectly fine, but the controller disconnected, and they can't command the sub to surface, wow, stupidity, my guess is, they got near the wreck/seabed, kicked up dust, which interfered with the controller signal, and thats it, one of them had better step outside and press the bluetooth sync button on the engines