Transport on the polar shelf (6)
Solution – sledge
This is a "literally so" clue. The whole clue can be taken to mean "sledge" as well as being able to break the clue up into its constituent parts.
Sledges were used as transport on the polar shelf
They are also a more general form of transport
And "polar" is also either "n" or "s" for north or south. In this case if you add a word for "shelf" ie "ledge" to s, you get "sledge".
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