Gunsen were folding fans used by warriors to cool themselves, made of wood or metal spokes, usually hung from the belt or breastplate.
Tessen were folding fans made of heavy plates of iron designed to look like normal, harmless closed fan, taken to places where weapons were not allowed.
Also used for fending off arrows, as a throwing weapon, and as an aid in swimming!!!(quote Wikipedia)
Gunpai were large solid open iron or solid wood fans, carried by high-ranking officers also used for signalling troops.
(Quoting Wikipedia again) "Araki Murashige is said to have used a tessen to save his life when the great warlord Oda Nobunaga sought to assassinate him. Araki was invited before Nobunaga, and was stripped of his swords at the entrance to the mansion, as was customary. Nobunaga intended to have the room's sliding doors slammed shut onto Araki's neck, killing him. However, Araki supposedly placed his tessen in the grooves in the floor, blocking the doors from closing."
