Gantoku Line

Construction began from the Iwakuni end. On 5 April 1929 the short Marifu–Iwakuni section opened as the Gantoku Line, and the station then called Iwakuni (now Nishi-Iwakuni) entered service. When work started from the western end as well, the existing stretch was renamed the Gantoku East Line on 29 May 1932, the same day the Gantoku West Line opened between Kushigahama and Suō-Hanaoka. The two halves were then extended toward each other through the hills, the western line reaching Takamizu in March 1934.

The gap was closed on 1 December 1934, when the Iwakuni–Takamizu section opened and the route ran through for the first time. At that moment the whole line was absorbed into the Sanyō Main Line as a new, shorter trunk alignment between Iwakuni and Kushigahama, and the older coastal route by way of Yanai was demoted, being separated off and redesignated the Yanai Line. For just under a decade the Gantoku alignment carried the main San'yō trunk traffic, crossing the watershed through the 3,149-metre Kinmeiji tunnel and six others.

The inland route proved an awkward trunk line. When double-tracking of the Sanyō Main Line was planned, the Gantoku alignment's steep grades and curves, and the need to bore a second long tunnel alongside the Kinmeiji tunnel, made it impractical to widen. The doubling was therefore carried out along the original coastal route through Yanai instead. On 11 October 1944 the coastal Yanai Line was reinstated as the Sanyō Main Line, and the inland section from Iwakuni to Kushigahama was separated off once more and formally became the Gantoku Line — reverting, after its brief main-line career, to the branch it has remained ever since.

Under Japanese National Railways the line settled into quiet local service. Diesel railcars were introduced on 16 April 1956, and the line acquired a junction when the Iwabi Line (today the Nishikigawa Railway's Seiryū Line) opened from Kawanishi on 1 November 1960. Steam haulage ended at the start of March 1971 in favour of diesel locomotives and railcars, all freight working ceased on 1 October 1974, and centralised traffic control governed from Hiroshima was commissioned across the whole line on 10 March 1982.

With the privatisation and break-up of Japanese National Railways on 1 April 1987, the entire Gantoku Line passed to the newly formed West Japan Railway Company, which has operated it ever since. JR West introduced one-man operation on most trains from 14 March 1992 and added several new stations over the years, so that the line came to serve fifteen.

The line carries only all-stations local trains; no rapid or limited-express services are scheduled over it. The torrential rains of July 2018 forced a complete suspension from 6 July, with the Iwakuni–Suō-Takamori section reopening on 20 August and the remaining Suō-Takamori–Kushigahama section on 22 September 2018. With traffic densities since reported below 2,000 passengers per day, the Gantoku Line is today a lightly used rural route whose future JR West has raised for discussion with the local municipalities.

• 19295 April: the Marifu–Iwakuni section opens as the Gantoku Line; the station then named Iwakuni (now Nishi-Iwakuni) enters service.
• 193229 May: the Gantoku West Line opens between Kushigahama and Suō-Hanaoka; the existing eastern stretch is renamed the Gantoku East Line the same day.
• 193428 March: the western line is extended from Suō-Hanaoka to Takamizu (11.0 km).
• 19341 December: the Iwakuni–Takamizu section opens, completing the through route; the whole line is absorbed into the Sanyō Main Line as a shorter trunk alignment, and the old coastal route via Yanai is separated off as the Yanai Line.
• 19421 April: Marifu Station is renamed Iwakuni, and the former Iwakuni Station is renamed Nishi-Iwakuni.
• 194411 October: the double-tracked coastal Yanai route is reinstated as the Sanyō Main Line; the Iwakuni–Kushigahama inland section is separated off again and formally becomes the Gantoku Line (43.7 km).
• 195616 April: diesel railcar service begins on the line.
• 19601 November: the Iwabi Line (today the Nishikigawa Railway Seiryū Line) opens from Kawanishi, giving the Gantoku Line a junction.
• 1971Steam haulage ends (late February) and is replaced from 1 March by diesel locomotive and railcar operation.
• 19741 October: all freight services on the line are discontinued.
• 198210 March: centralised traffic control (CTC), directed from Hiroshima, is commissioned over the entire line.
• 19871 April: with the privatisation and break-up of Japanese National Railways, the West Japan Railway Company (JR West) inherits the entire Gantoku Line.
• 199214 March: JR West introduces one-man operation on most trains.
• 2018The July 2018 rains suspend the whole line from 6 July; Iwakuni–Suō-Takamori reopens on 20 August and Suō-Takamori–Kushigahama on 22 September.
• 202211 April: in JR West's disclosure of line finances, the Gantoku Line is reported with a transport density below 2,000 passengers per day; on 27 April the company seeks discussions with local municipalities about its future.