Idiots in European port missing an entrance to shipping (6)

I believe the answer is:

twerps

'idiots' is the definition.
(both can mean stupid people)

I can't explain the remainder of the clue.

(Other definitions for twerps that I've seen before include "Foolish people" , "Nincompoops" , "Idiots!" .)

I've seen this clue in The Guardian.

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