After the end of World War II,  Yōji Watanabe, a former soldier of the Japanese Imperial Army’s naval unit, became an architect. He designed several notable, unique buildings that earned him the epithet “Mad Architect.”

One example of Watanabe’s unorthodox architectural designs can be found in the Shinjuku district of central Tokyo. Gunkan Higashi Shinjuku (formerly New Sky Building) is a 14-story building that is more commonly known as the Gunkan Biru (Battleship Building). As its nickname suggests, the building was designed to resemble a modern battleship. It has portholes for windows and a rooftop water tank that resembles the bridge of a ship. Completed in 1970, it was used for offices and residences.

Over the following four decades, however, the building grew decrepit. Though demolition was briefly considered, the structure was renovated and renamed Gunkan Higashi-Shinjuku Building. It is now a complex of condos, offices, and a gallery space. The building's color scheme has been changed, too, from stark gunmetal—which gave it another nickname, Iron Mansion—to mint green and grey. Today, it's considered one of the most significant examples of modern architecture in Tokyo.