For infantry, quite so. perhaps.
But not in this case. SSN=Submersible Ship, Nuclear

In cold winters, for instance, I cannot imagine soldiers wanting to shave or cut their hair, since extra hair would add warmth. Assuming the winter clothing is unavailable or inadequate.

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In cold winters, for instance, I cannot imagine soldiers wanting to shave or cut their hair, since extra hair would add warmth. Assuming the winter clothing is unavailable or inadequate.

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Never been in the military, but I have had beards and longer hair. In extreme cold weather, it DOES NOT add warmth. Same with a full head of hair. There just isn't enough hair and it is not of the texture to trap a significant amount of insulating air to reduce discomfort in extreme weather. Humans never really needed to adapt biologically to changing environments beacaue by the time those environments were encountered, the species had learned to use animal skins as protection from the cold. Animals who survived extreme conditions either evolved shedding coats of fur or multiple layers of different types of hair to insulate themselves. Even bird feathers on the smallest over wintering birds provide a great deal of insulation.