Kūkō Line

The line grew out of post-war planning for mass transit in northern Kyūshū. In March 1971 the Council for Urban Transport submitted Report No. 12 to the Minister of Transport, setting out a basic plan for passenger transport in the metropolitan area centred on Fukuoka and Kitakyūshū that included building the subway. Fukuoka City applied for a local-railway licence for the Meinohama–Hakata route on 1 February 1974 and obtained it on 22 August 1974, and a groundbreaking ceremony was held on 12 November 1975, beginning construction.

The first section opened on 26 July 1981, when Line 1 began carrying passengers between Muromi and Tenjin. Less than a year later, on 20 April 1982, the line was extended one stop east from Tenjin to Nakasu-Kawabata, and through-running began there with the Hakozaki Line (Line 2). On 22 March 1983 two further extensions opened on the same day — westward from Muromi to Meinohama, and eastward from Nakasu-Kawabata to a provisional Hakata station — and on that date mutual through-service began with the Japanese National Railways Chikuhi Line at Meinohama, linking the subway with the conventional line running west along the coast toward Karatsu.

The young line was an early proving ground for driver-only operation. After several phases of trials with empty and then revenue trains through 1981, 1982 and 1983, the subway began regular one-man operation on 20 January 1984 — described as the first such operation by a subway in Japan, although JNR through-trains were excluded from it. The eastern terminus was then finished in stages: the provisional Hakata station was replaced by the permanent main Hakata station on 3 March 1985, and double-track running on the approach to Hakata followed that July.

Extending the line the last few kilometres to Fukuoka Airport took the rest of the decade to arrange and build. The city applied to the Ministry of Transport in August 1986 for a railway licence for the Hakata–Fukuoka Airport section, received it that October, and gained construction approval in March 1987. Civil works began in September 1987 and went into full construction in May 1988. The Hakata–Fukuoka Airport section finally opened on 3 March 1993, completing the line as it runs today; with the airport reached, Line 1 took on the nickname "Airport Line."

In the years that followed, the line was steadily modernised and re-woven into the city's growing network. On 23 March 2002 the last trains were retimed later and the section over which Fukuoka City Subway cars ran through onto the Chikuhi Line was extended west to Chikuzen-Fukae. Platform-edge doors were progressively fitted, with installation completed at every station on 13 March 2004 when they entered service at Meinohama. The opening of the separate Nanakuma Line (Line 3) on 3 February 2005 created an interchange between the Airport Line at Tenjin and the new line at Tenjin-Minami.

The network ties tightened further over the following two decades. The Hayakaken IC card was introduced across all stations on 7 March 2009, and station numbering was displayed line-wide, together with the Hakozaki and Nanakuma lines, from 2 March 2011. When the Nanakuma Line was extended from Tenjin-Minami to Hakata on 27 March 2023, Hakata became a paid-area transfer between the two lines and the earlier out-of-gate transfer arrangement at Tenjin was discontinued. New 4000 series trains entered service on the line on 29 November 2024.

• 1971March: the Council for Urban Transport submits Report No. 12 to the Minister of Transport, a basic plan for the Fukuoka–Kitakyūshū metropolitan area that includes building the subway.
• 19741 February: Fukuoka City applies for a local-railway licence for the Meinohama–Hakata route; the licence is granted on 22 August.
• 197512 November: a groundbreaking ceremony is held and construction begins.
• 198126 July: the first section opens — Line 1 begins service between Muromi and Tenjin.
• 198220 April: the line is extended from Tenjin to Nakasu-Kawabata, where through-service with the Hakozaki Line (Line 2) begins.
• 198322 March: Meinohama–Muromi and Nakasu-Kawabata–(provisional) Hakata extensions open the same day; mutual through-service with the JNR Chikuhi Line begins at Meinohama.
• 198420 January: regular one-man (driver-only) operation begins — described as the first such operation by a subway in Japan (JNR through-trains excluded).
• 19853 March: the permanent main Hakata station opens, replacing the provisional Hakata station; double-track running toward Hakata follows in July.
• 19874 April: with the privatisation of JNR, the through-service partner Chikuhi Line passes to JR Kyūshū. 13 September: construction of the Hakata–Fukuoka Airport section begins (the licence for it had been applied for in August 1986 and granted that October).
• 19933 March: the Hakata–Fukuoka Airport section opens, completing the line; Line 1 takes on the nickname "Airport Line."
• 200223 March: last trains are retimed later and the Fukuoka City Subway through-running section on the Chikuhi Line is extended west to Chikuzen-Fukae.
• 200413 March: with platform doors entering service at Meinohama, installation is completed at every station.
• 20053 February: the Nanakuma Line (Line 3) opens, creating an interchange between the Airport Line at Tenjin and Tenjin-Minami.
• 20112 March: station numbering is displayed line-wide, together with the Hakozaki and Nanakuma lines. (IC card Hayakaken had been introduced at all stations on 7 March 2009.)
• 202327 March: with the Nanakuma Line extended to Hakata, Hakata becomes a paid-area transfer between the two lines and the out-of-gate transfer at Tenjin is discontinued.
• 202429 November: 4000 series trains enter service on the line.