Meitetsu Komaki Line

The line was not built by the state but by Meigi Railway (名岐鉄道), one of the predecessor companies of today's Nagoya Railroad. In 1931 Meigi Railway consolidated the railway concessions of two earlier ventures — Jōhoku Electric Railway (城北電気鉄道) and Bihoku Railway (尾北鉄道) — to assemble the route. The corridor ran along the old Kami-kaidō highway, a district that had failed in the Meiji era to attract the Chūō Main Line, so a railway here was a long-held local wish.

The first section, between Kamiiida and Shinkomaki (the present Komaki Station), opened on 11 February 1931 as the Jōhoku Line (城北線). The line was not electrified at first and was worked by gasoline railcars (the Kibo 50 type). On 29 April 1931 the remaining segment from Shinkomaki to Inuyama opened, completing the route, and the Kamiiida–Inuyama line was renamed the Ōsone Line (大曽根線). A planned extension from Kamiiida toward Higashi-Ōsonechō never materialised.

The Second World War reshaped the line. As gasoline supply grew difficult, the Kamiiida–Shinkomaki section was electrified on 1 July 1942, though as the war deepened many stations were suspended. On 1 May 1945 Shinkomaki Station was renamed Komaki. After the war, on 24 November 1947, the Komaki–Inuyama section was electrified, completing electrification of the whole line. On 16 May 1948 the Ōsone Line was renamed the Komaki Line (小牧線), and the older line that had until then carried the name "Komaki Line" (the Iwakura–Komaki route) became the Iwakura Branch Line.

The line saw a series of upgrades over the following decades. In 1954 Meitetsu introduced its first single-track automatic block working here, and rolled out centralised traffic control (CTC) across the whole line by 1956 — among the operator's earliest uses of the system. On 1 October 1964 the overhead voltage was raised from 600 V to 1,500 V DC. The line was then double-tracked in stages, beginning with the Manai–Komaki section in 1977 and continuing through grade-separation and continuous elevated works around Komaki over the following decades.

For years the Komaki Line was awkwardly cut off at its Nagoya end. After the Iwakura Branch Line closed in 1964 and the Nagoya city tram's Onarimichi line closed in 1971, Kamiiida was left connected only to buses, and commuters frequently walked the ten minutes to Heian-dōri Station on the Nagoya Municipal Subway Meijō Line rather than wait for unreliable buses. To fix this, the Kamiiida–Ajima section was placed underground and a new subway line, the Kamiiida Line, was built to link Kamiiida with Heian-dōri.

The through-connection opened in 2003. On 27 March 2003 a new double-track underground section from Kamiiida to Ajima (2.3 km, the Kamiiida Connecting Line) opened, replacing the former above-ground single track, and mutual through-running with the Nagoya Municipal Subway Kamiiida Line began, giving direct access to Heian-dōri on the Meijō Line and dramatically improving convenience. The underground Kamiiida–Ajima section is owned by the Kamiiida Connecting Line company, with Meitetsu operating as a Type II operator there, and the route's line colour on maps was changed from the green of the Inuyama Line to the pink of the Kamiiida Line.

Today the Komaki Line carries Meitetsu 300 series trains, with Nagoya Municipal Subway 7000 series sets working the through services. Only Komaki Station among the intermediate stops is staffed, the others being managed remotely under a station-management system introduced around the 2003 through-running, and the whole line accepts manaca and other nationally interoperable transit IC cards.

• 193111 February: Meigi Railway opens the first section, Kamiiida–Shinkomaki (now Komaki), as the Jōhoku Line, worked by non-electrified gasoline railcars.
• 193129 April: the Shinkomaki–Inuyama section opens, completing the route; the Kamiiida–Inuyama line is renamed the Ōsone Line.
• 19421 July: the Kamiiida–Shinkomaki section is electrified at 600 V DC, as wartime gasoline supply grows scarce.
• 19451 May: Shinkomaki Station is renamed Komaki.
• 194724 November: the Komaki–Inuyama section is electrified, completing electrification of the whole line.
• 194816 May: the Ōsone Line is renamed the Komaki Line; the former Iwakura–Komaki 'Komaki Line' becomes the Iwakura Branch Line.
• 19541 November: Meitetsu's first single-track automatic block working is introduced; CTC is commissioned on the Toyoyama–Komaki section, the operator's first use of centralised traffic control.
• 195610 February: CTC is extended to the Gakuden–Inuyama section, completing CTC coverage of the whole line.
• 19641 October: the overhead voltage is raised from 600 V to 1,500 V DC.
• 197729 May: the Manai–Komaki section is double-tracked, the first stage of the line's progressive double-tracking.
• 198923 April: continuous grade-separation between Manai and Komakihara is completed; Komaki Station is relocated underground.
• 19978 February: the Futago Signal Box–Ajiyoshi section is double-tracked as double-tracking advances northward.
• 200014 October: the Toyoyama Signal Box–Manai section is double-tracked.
• 200327 March: a new 2.3 km double-track underground section, Kamiiida–Ajima (the Kamiiida Connecting Line), opens, replacing the old surface track; mutual through-running with the Nagoya Municipal Subway Kamiiida Line begins, giving direct access to Heian-dōri on the Meijō Line. The line colour changes from green to pink.
• 201111 February: the manaca IC card system enters service on the line.