Perhaps our subs are capable of things you’re not thinking about.
Flying? Apparently the coldest temps anywhere in the ocean are around 28 degrees F.
For a submarine to reach an environment with a temp of 100 below zero, it would have to fly over 250,000 feet above the surface of the earth, higher than an SR71 could fly.
Exactly. Sure, the outer hull may not be subjected to water below 28 degrees. But they do occasionally surface in arctic conditions. Outside air temps can get much colder.
Also, these were castings. No idea if it has anything to do with external running gear, or some internal equipment. Maybe there are things inside that need cryogenic level cooling... If that cooling fails, the equipment is offline/unavailable, potential mission kill.