From Ikebukuro toward central Tokyo
After the Second World War, population growth in Tokyo’s northwestern suburbs increased commuter flows into Ikebukuro on the Tōbu Tōjō and Seibu Ikebukuro lines. The national railway’s Yamanote Line carried onward traffic, with its Ikebukuro–Ōtsuka section particularly crowded. A revised rapid-transit plan in 1946 proposed five routes. The Teito Rapid Transit Authority prioritized Line Four, the Marunouchi Line, initially planning a 7.7-kilometer section from Ikebukuro to Kanda.
Financing accompanied the engineering difficulties. Allocation of counterpart funds from aid to Japan initially favored coal, electricity and other industries, while the subway proposal lacked completed detailed designs. Financial negotiations stalled. Prospects for funding emerged by late 1949, the construction plan gradually took shape, and work began on April 20, 1951.
Changing the terminus and using surface sections
Kanda did not become the first-stage terminus. Narrow streets constrained the proposed underground station south of the national railway’s Ochanomizu station; suitable construction roads were also lacking between Kanda and Tokyo. The authority moved Ochanomizu station to the north bank of the Kanda River, abandoned the proposed Ginza Line interchange at Kanda and revised the first phase to Ikebukuro–Ochanomizu in November 1952.
The subway used shallow tunneling where possible. Following the terrain between the Kōrakuen lowland and adjoining plateaus produced about 1.8 kilometers of surface sections between Myōgadani and Hongō-sanchōme, with a surface depot near Myōgadani. The 1954 outline’s map used different colors for tunnel and surface tracks, showing successive structural forms along a single line.
Economizing on civil works and changing site methods
President Kiyohide Suzuki discouraged grand or elaborate facilities, keeping station works tightly controlled. Initial platforms were about eighty meters long for four-car trains, with structural provision for six cars later. Some retaining works used stone, while depot and storage tracks had lighter rails than the main line, concentrating expenditure on essential facilities.
Construction mainly used cut-and-cover: excavating from the surface, building underground structures and restoring the cover. The authority purchased ready-mixed concrete centrally from specialist suppliers, replacing separate on-site mixing by individual contractors. Concrete pumps and pipelines near the prison and elsewhere reduced manual handling. The original outline recorded 17,700 tonnes of steel, 83,000 cubic meters of ready-mixed concrete and total construction expenditure of ¥5.25 billion. Materials, equipment and work organization determined how construction could proceed in the city.
Opening in 1954 and the 300-series trains
The Ikebukuro–Ochanomizu section opened for passenger service on January 20, 1954. Its 6.4 kilometers connected the terminals through Shin-Ōtsuka, Myōgadani, Kōrakuen and Hongō-sanchōme. Three-car trains ran about every three minutes thirty seconds during busy periods and every four minutes otherwise. End-to-end travel took about eleven minutes thirty seconds, with a flat ¥15 fare matching the Ginza Line.
The line used 1,435-millimeter standard gauge, 600-volt DC third-rail power and automatic train-stop equipment. The new 300-series trains reduced combustible material with all-steel bodies. Double-leaf doors supported rapid boarding and alighting. The construction outline also listed fluorescent lighting, emergency communication equipment and resilient wheels. Safety and passenger conditions remained design priorities alongside savings in civil works.
Extensions and an interchange network
The line extended in stages after its first opening: to Awajichō and Tokyo in 1956, Nishi-Ginza in 1957, Kasumigaseki in 1958 and Shinjuku in March 1959. The full 16.6-kilometer Ikebukuro–Shinjuku section then operated. The Ginza Line interchange originally planned at Kanda was later achieved at Akasaka-mitsuke with cross-platform transfers in the same direction.
West of Shinjuku, an extension was built as the Ogikubo Line, with the Hōnanchō branch also supporting access to the Nakano depot. Both parts opened progressively in 1962, and the Ogikubo Line name was incorporated into the Marunouchi Line in 1972. Trains grew from three to six cars. A route relieving traffic pressure at Ikebukuro developed into a network connecting residential districts, commercial centers and central interchanges.
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