Sasebo Line

The corridor was one of the earliest pieces of the railway network in western Kyushu. The private Kyushu Railway opened the section from Saga to Takeo (present-day Takeo-Onsen) on 5 May 1895 as part of its original Nagasaki Line. The company pushed on, extending the line from Takeo to Haiki on 10 July 1897 and from Haiki on to Sasebo on 20 January 1898, giving the naval port of Sasebo its rail connection. For its first decades this Saga–Haiki–Sasebo route was the trunk approach toward both Nagasaki and Sasebo.

Like most of Japan's early private trunk railways, the Kyushu Railway was taken into public ownership: it was nationalised on 1 July 1907 under the railway nationalisation policy. The name "Sasebo Line" first appeared on 12 October 1909, when the government railways designated the Haiki–Sasebo segment as a separate line. Over the following decades a number of stations and signal posts were added along the route, and in 1913 the junction station then called Yamaguchi was renamed Hizen-Yamaguchi.

The line took on its modern shape in the 1930s. On 1 December 1934 a new, more direct Nagasaki Main Line opened between Hizen-Yamaguchi (present-day Kōhoku) and Isahaya, and at the same time the Hizen-Yamaguchi–Sasebo route was designated the Sasebo Line. The portion of railway continuing beyond Sasebo was split off to become the Matsuura Line. Through the war years and afterwards further stations and signal posts along the line were opened or upgraded.

Under Japanese National Railways the Sasebo Line was modernised in the 1970s and 1980s. Takeo Station was renamed Takeo-Onsen on 19 June 1975, electrification work that had begun in 1973 was completed on 6 June 1976 when the whole Hizen-Yamaguchi–Sasebo section was energised, and freight operations were progressively wound down, beginning with the Haiki–Sasebo segment in 1985. With the division and privatisation of Japanese National Railways on 1 April 1987, the line passed to the newly formed JR Kyushu.

In the twenty-first century the Sasebo Line gained a new strategic role as a feeder to high-speed rail. The Ōmachi–Takahashi section was double-tracked, completed on 27 February 2022, to accommodate a faster service, and on 23 September 2022 — the day the Nishi-Kyushu Shinkansen opened between Takeo-Onsen and Nagasaki — Hizen-Yamaguchi Station was renamed Kōhoku and the line was upgraded for higher speeds. The limited express "Relay Kamome" now runs between Kōhoku and Takeo-Onsen, where passengers transfer across the platform to the Shinkansen, making the Sasebo Line a key link in the relay system that connects the Nagasaki bullet-train line to the rest of the Kyushu network.

• 18955 May: the Kyushu Railway opens the Saga–Takeo (present-day Takeo-Onsen) section as part of its original Nagasaki Line.
• 189710 July: the line is extended from Takeo to Haiki.
• 189820 January: the line is extended from Haiki to Sasebo, reaching the naval port.
• 19071 July: the Kyushu Railway is bought out and nationalised under the railway nationalisation policy.
• 190912 October: the government railways designate the Haiki–Sasebo segment as the separate 'Sasebo Line' — the first use of the name.
• 19131 March: the junction station then called Yamaguchi is renamed Hizen-Yamaguchi.
• 19341 December: a new Nagasaki Main Line opens between Hizen-Yamaguchi (present-day Kōhoku) and Isahaya, and the Hizen-Yamaguchi–Sasebo route is designated the Sasebo Line; the section beyond Sasebo becomes the Matsuura Line.
• 197519 June: Takeo Station is renamed Takeo-Onsen.
• 19766 June: the entire Hizen-Yamaguchi–Sasebo line is electrified at 20 kV 60 Hz AC, completing work begun in 1973.
• 198514 March: freight operations are abolished between Haiki and Sasebo.
• 19871 April: with the division and privatisation of Japanese National Railways, the line passes to JR Kyushu.
• 202014 March: through services to the Matsuura Railway are discontinued.
• 202227 February: the Ōmachi–Takahashi section is double-tracked ahead of the timetable revision and speed-up.
• 202223 September: the Nishi-Kyushu Shinkansen opens between Takeo-Onsen and Nagasaki; Hizen-Yamaguchi Station is renamed Kōhoku and the line is upgraded for higher speeds, with the 'Relay Kamome' limited express connecting at Takeo-Onsen.