NHK has learned that only two of the 12 remaining historical castles in Japan with a wooden keep are equipped with sprinklers.
The castles are designated either national treasures or important cultural properties.
An investigation by NHK revealed that only Himeji Castle in Hyogo Prefecture and Matsue Castle in Shimane Prefecture have sprinklers to protect the structures from burning down.
The reasons why the rest don't have them vary. In the case of five castles, officials said that installing sprinklers could damage the properties.
Officials at some castles said that because they are on top of hills, it is difficult to supply water to them. Others said that the weight of a sprinkler system would pose problems for anti-earthquake technology.
Two castles do not have smoke detectors, either.
The revelations come in the wake of a fire that destroyed Shuri Castle in Okinawa, southern Japan, on October 31.
The iconic structure did not have sprinklers, and the main building where the blaze is believed to have started did not have smoke detectors, which can detect fire earlier than flame or heat sensors.
Experts say the fire-proof measures at the castle were inadequate.