The 3 water buses operated by the Tokyo Mizube Cruising Line also have a duty as disaster prevention boats. They are utilized as passenger boats primarily on the Sumida River and in the Port of Tokyo during normal times in order to be deployable as disaster prevention boats during times of emergency. Passengers may enjoy the tranquil passing of time through mini-cruises on the water buses, and volunteer river guides provide tours which add an essential ingredient to the cruises’ charms.