Futtsu is a city located in Chiba Prefecture, Japan. As of 1 November 2020, the city had an estimated population of 42,476 in 18,115 households and a population density of 210 persons per km2. The total area of the city is 205.53 square kilometres (79.36 sq mi).

Tokyo Bay Fortress was the name of a group of coastal fortifications built to guard the entrance to Tokyo Bay and thus the city of Tokyo from attack from the sea. These gun batteries and fortifications ceased to be used after the end of World War II.