Tessen

The Tessen, (lit. "Iron Fan" or War Fan), is a folding fan with outer spokes made of heavy plates of iron which were designed to look like normal, harmless folding fans or solid clubs shaped to look like a closed fan.

Samurai could take these to places where swords or other overt weapons were not allowed, and some swordsmanship schools included training in the use of the tessen as a weapon. The tessen was also used for fending off arrows and darts, as a throwing weapon, and as an aid in swimming.

A war fan is a fan designed for use in warfare. Several types of war fans were used by the samurai class of feudal Japan.

Trivia

 * As of the events of "Baxter's Gambit", April is now armed with a Tessen, (鉄扇; lit. a "Iron Fan", better known as a Japanese war fan), a weapon that Splinter had one day hoped to give to his daughter, Miwa, who April reminds him of. April will now be focusing her fighting style around the real-life Japanese martial art of Tessenjutsu.