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"How to Command a Nuclear Submarine" available on Prime Video.

looks like there is a newer version (more recent) following potential sub commanders for the royal navy called "Submarine School". 4 parts, all are on YT. there is even a US navy submariner among the potential captains!

part 1: > https://www.youtube.com/watch?v=1dZBNFFaDkY

Search for "Submarine School Episode <episode N>of4" for the rest.

YouTube suggests this as part 2: https://www.youtube.com/watch?v=fL5AW0enIRA

I don't think it is the same series. The Perisher series focused almost exclusively on the candidates and The Teacher.