Senseki Line

The line was not built by the state but by a private company, the Miyagi Electric Railway (宮城電気鉄道), which was established in 1922. The company opened its line in stages from Sendai eastward toward the coast. The first section, between Sendai and Nishi-Shiogama, opened on 5 June 1925, and the railway then extended to Hon-Shiogama in 1926 and to Matsushima-Kōen (today's Matsushima-Kaigan) in 1927. Service reached Rikuzen-Ono in April 1928 and finally Ishinomaki on 22 November 1928, completing the through route between Sendai and Ishinomaki.

From the outset the Miyagi Electric Railway was technically ambitious. To reach central Sendai it bored a tunnel and opened the Sendai–Higashi-Shichibanchō section as an underground railway — by Japanese accounts the first commercial underground railway in the country, predating the opening of Tokyo's Ginza Line subway by about two and a half years. The company had been conceived in part to make use of surplus electricity, and electric operation was a defining feature of the line from its opening, a legacy that survives in its present-day 1,500 V DC system.

During the Second World War the line was taken into state ownership. On 1 May 1944 the Miyagi Electric Railway was nationalised through a wartime compulsory purchase, and it was at this point that the route received the name "Senseki Line." The nationalisation was driven by the war effort: the line served the transport of materiel and the commuting of workers tied to military facilities in the area, including the Tagajō naval arsenal and the Yamoto airfield. Under the Japanese National Railways (JNR) the line was progressively upgraded, with double-tracking carried out across much of the route between the late 1960s and 1981. When JNR was broken up and privatised on 1 April 1987, the Senseki Line passed to JR East.

The most significant infrastructure change of the JR era came at the Sendai end. On 11 March 2000 the Sendai Tunnel opened, moving the surface section between Sendai and Rikuzen-Haranomachi underground and adding a short new stretch to a new terminus, Aoba-dōri Station, in the heart of the city near the Sendai subway. This put the busy inner end of the line below ground and gave the Senseki Line its present-day starting point.

The line was devastated by the Tōhoku earthquake and tsunami of 11 March 2011. Because a large share of the route — by Japanese estimates roughly 68 percent — ran close to the coast, it suffered severe damage from both the quake and the tsunami: hundreds of points of track deformation, more than three kilometres of track washed away, and many damaged station buildings. A train was derailed and swept away between Nobiru and Tōna, and another set was inundated at Ishinomaki. Services were halted across the line, and restoration came only in stages: the inner Sendai section reopened within weeks, the Yamoto–Ishinomaki section was restored with diesel trains in July 2011, and the Rikuzen-Ono–Yamoto section followed in March 2012, leaving only the worst-hit central portion closed.

For that surviving gap, JR East chose to rebuild on a safer alignment, relocating roughly 6.4 kilometres of the line between Rikuzen-Ono and Rikuzen-Ōtsuka about 500 metres inland. The full Senseki Line finally reopened on 30 May 2015. The same day saw the debut of the Senseki-Tōhoku Line, a new through service made possible by a short connecting line built between the Senseki Line and the parallel Tōhoku Main Line near Shiogama; JR East introduced new HB-E210 series two-car hybrid diesel-electric trains for it. By routing Sendai–Ishinomaki trains over the faster Tōhoku Main Line for part of the journey, the new service cut the Sendai–Ishinomaki travel time by roughly ten minutes, to about an hour.

• 1922The Miyagi Electric Railway (宮城電気鉄道) is established to build the line.
• 19255 June: the Miyagi Electric Railway opens the first section, Sendai–Nishi-Shiogama; the Sendai–Higashi-Shichibanchō stretch opens as, by Japanese accounts, Japan's first commercial underground railway.
• 192614 April: the line is extended from Nishi-Shiogama to Hon-Shiogama.
• 192718 April: the line is extended from Hon-Shiogama to Matsushima-Kōen (now Matsushima-Kaigan).
• 192822 November: the Rikuzen-Ono–Ishinomaki section opens, completing the through line between Sendai and Ishinomaki (earlier that year, on 10 April, the line had reached Rikuzen-Ono).
• 19441 May: the Miyagi Electric Railway is nationalised by wartime compulsory purchase and the route is renamed the Senseki Line, serving military-related transport in the area.
• 19811 November: the Nishi-Shiogama–Higashi-Shiogama section is elevated and double-tracked, near the end of a double-tracking programme carried out from the late 1960s.
• 19871 April: with the breakup and privatisation of Japanese National Railways, the Senseki Line becomes part of JR East.
• 200011 March: the Sendai Tunnel opens; the Sendai–Rikuzen-Haranomachi surface section is moved underground and a new section to Aoba-dōri Station opens as the line's new terminus.
• 201111 March: the Tōhoku earthquake and tsunami devastate the line — with much of the route near the coast, hundreds of points of track deformation, over 3 km of track washed away, and many damaged stations; a train is swept away between Nobiru and Tōna.
• 201116 July: the Yamoto–Ishinomaki section reopens, operated with diesel trains, as part of the staged restoration after the tsunami.
• 201217 March: the Rikuzen-Ono–Yamoto section reopens, leaving only the worst-hit central portion of the line still closed.
• 201530 May: the full Senseki Line reopens after the Rikuzen-Ono–Rikuzen-Ōtsuka section (~6.4 km) is rebuilt about 500 m inland; the same day, the Senseki-Tōhoku Line through service begins via a new connecting line to the Tōhoku Main Line near Shiogama, using new HB-E210 hybrid trains and cutting the Sendai–Ishinomaki time by about 10 minutes.
• 201626 March: Ishinomakiayumino Station opens between Rikuzen-Yamashita and Ishinomaki.