Prefabricated building with a corrugated iron roof, first produced in WWI (6,3)

I believe the answer is:

nissen hut

(Other definitions for nissen hut that I've seen before include "Military shelter made of corrugated steel" , "Corrugated iron construction" , "army building" , "Prefabricated corrugated iron dwelling" , "Prefab" .)

I've seen this clue in The Guardian.

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