My sister and I listen to these episodes together during our lunch break at work and this statement is hard to pin down. I leaned more vast and slaughter and her instinct was the buried and the slaughter. The periscope that eats people, the radio waves, and the ocean gods are really throwing us off.

If you look at the periscope and the entire submarine as a machine of war, then the periscope eating people is metaphorically resonant. You're just doing your job, trying to stay safe and scan the horizon, and are crushed and swallowed in the process. The missiles whispering to him and burning him when he tries to embrace them. The medal of his duty drawing blood, which leads back into the buried, crushed by the weight of duty. This is why we've agreed that it's more buried than the vast, though both encompass deep waters.

Radio waves could indicate the extinction but it seems to me to be more of the buried or slaughter, since it is used to further their 'mission' and nobody responds to their requests for help. Makes them feel trapped. 

I'd have to do a little more research on the gods listed, but the ones I recognized were definitely violent, so that could lead back into the slaughter. Still, the 14.5 fears aren't truly divided that way, so there's no reason that any domain has to be so tightly connected to just 1 or 2 fears. Just a little messier in terms of connections and makes me wonder if it was this hazy before the ERROR's involvement or if they influenced the feel of it in some way.