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A retractable sword was a hand-held weapon, with a blade that could be retracted by pressing a button on the hilt. When sheathed, the blade was entirely contained within the hilt, making it small, compact and easy to carry. When released, the blade extended rapidly to a length of approximately one meter by unfolding in segments.
In form when fully extended, the sword resembled a Katana, a traditional Japanese sword.
Hikaru Sulu owned a retractable sword and used it on the Narada's drill platform above Vulcan in 2258, to fight off a pair of Romulans. (Star Trek)
In the script of Star Trek, Sulu instead "kick[ed] off an antenna piece" which he proceeded to use "as a saber."