Nanban-bo is a tool designed for catching and restraining an opponent. It has a long pole of approximately 2.2 meters, at the end of which there is a mechanical device that operates a pair of iron arms. When open, the arms resemble the shape of the letter "U" but when pressed against an object the arms close abruptly and grab hold of the object.
Long pole weapons for grabing an oponent on the battlefield are known since the early medieval period as can be seen, for example, in the Mongol Invasions Picture Scrolls. At that time the Japanese forces used the kumade 熊手 to take down an enemy combatant from a safe distance, then attack him with a sword or naginata.
By the Edo period, and with the develpment of an organized police force, such long-pole offensive weapons were replaced by tools of somewhat similar features that were designed for the purpose of subdueing and restraining a roudy criminal. These were know as bansho rokugu 番所六具(6 police tools), among which were the primary torimono sandogu 捕者三道具(3 tools for catching a person): sode garami 袖搦, sasumata 刺又, and tsukubo 突棒.
Nanban-bo seems to be an improved mechanical version of the sasumata. Since the sixteenth cetury the name "nanban" refers to foreign coutries or items, suggesting that Nanban-bo is an imported tool. However, the similarity to the widely used sasumata, both in shape and in function, is an indication that the Japanese adopted the concept of moving parts and the mechnism that operates them.
In any case, the Nanban-bo must have been more effective than the sasumata because the snap of the iron arms on a limb delivered a shocking pain, and also because, unlike the sasumata that was effective only when pushing the limb, it allowed the handler to pull the opponent after the arms closed tightly on the limb. The main downside of the sasumata was probably the cost and difficulty in production, which may explain why it is a rare tool to come by. A simplified smooth version of the sasumata, on the other hand, is still used today as a standard tool for the Japanese riot police, but can also be found in any police station for special activity purposes.
The following video demonstrates the employment of Nanban-bo to catch and restratin a sword wielding attacker. The Nanban-bo used for the demonstration is an authentic Edo period Nanban-bo, which necessitated especially carefull application. Nevertheless, one can clearly appreciate how effective it was for the purpose it was designed.