The original concept for the Reliant was closely based on the Enterprise, since after all, they were sister ships. One concern with this similarity was that it might make it difficult for audiences to tell the two ships apart. Producer Harve Bennett came to the rescue with a suggestion that the Reliant's warp engines might be hung below the saucer, rather than mounted above. In effect, Bennett made the Reliant an upside-down version of the Enterprise. The low-slung engines gave Khan's ship its sleek visual identity, and helped make it one of the most memorable guest ships in any Star Trek film.