NPX?

The airport code for the skiway at the South Pole is NPX which seems somewhat odd for the South Pole Station. (All airfields have such codes, many of them are obvious, SFO for San FranciscO, but some less so, ORD for Chicago O'Hare? Well, it was originally Orchard Field which was renamed for the WW2 fighter ace O'Hare, so it kept its old shorthand form.) Well, originally the South Pole Station was run by the Navy, and they named their airfields (well, the airfield shorthands) to all start with N for Navy. So, that's the Navy Pole Station (X). There's no airfield at the North Pole, so all is right in the world, right?