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Jim Martin's "early" sketch was actually done very recently, years after the
Defiant model and the sets were built. Jim says that he did not do any
research into the ship when he did the drawing, but he thought that by labeling
it as an "early" sketch, he could get away with any differences between the
sketch and what the show (including Doug) has actually done. (Jim was one of
the principal designers for the Defiant miniature, but he was not involved with
the final version of the model, having left the show shortly after he completed
his work.)

-Mike
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I think this is as clear an answer as it could be as far as the designer's intentions are concerned.