Aizu Line

The line began as a project of the Japanese National Railways (JNR), built between 1927 and 1953 as the northern part of a planned through route connecting Aizu-Wakamatsu with Tokyo; the matching southern section was eventually realised as the Yagan Railway Aizu Kinugawa Line. The first segment, from Nishi-Wakamatsu to Kamimiyori (now Ashinomaki-Onsen), opened on 1 November 1927, a distance of 10.5 km. Construction then advanced south in stages over the following decades.

The line reached Yunokami (now Yunokami-Onsen) on 22 December 1932 and Aizu-Tajima on 27 December 1934. After a wartime pause, the route was pushed on from Aizu-Tajima to Arakai on 12 December 1947, and the final segment from Arakai to Aizu-Takinohara opened on 8 November 1953, completing the line as the JNR Aizu Line. In December 1980, a 12.2-kilometre realignment between Ashinomaki-Onsen and Yunokami-Onsen opened to clear the way for construction of the Ōkawa Dam.

A pivotal change came with the south-end connection. On 9 October 1986 the line's terminus, Aizu-Takinohara, was renamed Aizu-Kōgen, and in the same year the third-sector Yagan Railway opened its Aizu Kinugawa Line, finally joining the Aizu Line to the railway network heading toward Tokyo via the Tōbu system. Despite this new link, JNR judged the Aizu Line an unprofitable secondary line and earmarked it for transfer to local interests.

With the privatisation of JNR on 1 April 1987 the line passed first to the East Japan Railway Company (JR East). JR East's tenure was brief: on 16 July 1987 its first-class railway operations on the line ceased and the third-sector Aizu Railway, established by local governments, took over the 57.4-kilometre Nishi-Wakamatsu–Aizu-Kōgen line. The handover was accompanied by a wholesale renaming of stations along the route — among them Kamimiyori to Ashinomaki-Onsen, Yunokami to Yunokami-Onsen, and Itozawa to Nanatsugatake-Tozanguchi — and Yunokami-Onsen's distinctive thatched-roof station building was completed at the end of that year.

Electrification followed in 1990. On 12 October 1990 the Aizu-Tajima–Aizu-Kōgen section was electrified at 1,500 V DC, and Aizu Railway began mutual through-running with the Yagan Railway and Tōbu Railway, opening direct services off the line toward the Tokyo area. Japan Freight Railway ended its operations over the line on 1 April 1999. On 18 March 2006 the southern terminus Aizu-Kōgen was renamed once more, to Aizukōgen-Ozeguchi, its present name.

In the twenty-first century the Aizu Line has leaned into tourism and through-services. The "AIZU Mount Express" began running on 23 March 2002, and from 17 March 2012 it extended through onto the Tōbu Nikkō Line as far as Tōbu-Nikkō; days later, on 25 March 2012, the open-car observation excursion train "Ozatoro Tenbō Ressha" began through-running to Kinugawa-Onsen on the Tōbu Kinugawa Line. A new limited express, the "Revaty Aizu" using Tōbu 500 series equipment, started on 21 April 2017, and from 12 March 2022 it became the only electric train operating on the Aizu Line. Today the electrified southern part carries services that continue beyond Aizukōgen-Ozeguchi onto the Yagan Railway, Tōbu and JR East all the way to Tokyo, while the non-electrified northern part runs diesel trains that continue beyond Nishi-Wakamatsu to Aizu-Wakamatsu on the JR East Tadami Line.

• 19271 November: JNR opens the first segment, Nishi-Wakamatsu–Kamimiyori (now Ashinomaki-Onsen), 10.5 km.
• 193222 December: the line is extended to Yunokami (now Yunokami-Onsen).
• 193427 December: the line is extended to Aizu-Tajima.
• 194712 December: the line is extended from Aizu-Tajima to Arakai.
• 19538 November: the final segment Arakai–Aizu-Takinohara opens, completing the JNR Aizu Line.
• 19801 December: a 12.2 km realignment between Ashinomaki-Onsen and Yunokami-Onsen opens, made for the construction of the Ōkawa Dam.
• 19869 October: the terminus Aizu-Takinohara is renamed Aizu-Kōgen; the same year the third-sector Yagan Railway opens its Aizu Kinugawa Line, connecting the line toward Tokyo.
• 19871 April: with the privatisation of JNR, the line passes to JR East.
• 198716 July: JR East's first-class operations on the line cease and the third-sector Aizu Railway takes over the 57.4 km Nishi-Wakamatsu–Aizu-Kōgen line; numerous stations are renamed (e.g. Kamimiyori→Ashinomaki-Onsen, Yunokami→Yunokami-Onsen).
• 198720 December: Yunokami-Onsen Station's thatched-roof station building is completed — one of only two thatched-roof stations in Japan.
• 199012 October: the Aizu-Tajima–Aizu-Kōgen section is electrified at 1,500 V DC, and mutual through-running with the Yagan Railway and Tōbu Railway begins.
• 19991 April: Japan Freight Railway (JR Freight) ends operations over the line.
• 200223 March: the 'AIZU Mount Express' service begins operating.
• 200618 March: the southern terminus Aizu-Kōgen is renamed Aizukōgen-Ozeguchi, its present name.
• 201217 March: the 'AIZU Mount Express' begins through-running to Tōbu-Nikkō on the Tōbu Nikkō Line. 25 March: the open-car observation train 'Ozatoro Tenbō Ressha' begins through-running to Kinugawa-Onsen on the Tōbu Kinugawa Line.
• 201721 April: the limited express 'Revaty Aizu', using Tōbu 500 series equipment, begins operating.
• 202212 March: the 'Revaty Aizu' becomes the only electric train operating on the Aizu Line.