From the wiki: “The Tōkaidō Main Line route takes its name from the ancient road connecting the Kansai region (Kyoto, Osaka) with the Kantō region (Tokyo, then Edo) through the Tōkai region (including Nagoya). Literally, it was the Tōkai road, or Road through Tōkai. The Tōkaidō railway does not follow the old road exactly, since the feudal highway diverged at Nagoya toward the Mie Prefecture coastline. Japan’s largest population centers are along the Tokaido: Tokyo, Yokohama, Nagoya, Kyoto, Osaka and Kobe.
“The ‘Tokaido Line’ name was formally adopted in 1895. Express service between Tokyo and Kobe began in 1896, sleeper service in 1900, and dining car service in 1901. In 1930 the first Tsubame (‘swallow’) express was introduced, reducing the Tokyo-Kobe travel-time to 9-hours – a significant reduction from the 20-hours required in 1889 and 15-hours in 1903.
“By 1956 electrification was completed along the Tokyo-Osaka section and with the introduction of new Kodama limited-express service [postcard image above] in 1958, travel time was reduced to 6-1/2 hours.
“Services used ‘151 Series’ trainsets – the first EMU train service of the Japanese National Railways to be classified as a limited express, the highest (fastest) train type at that time on the national railway system – which were the first rolling stock that enabled passengers to go and return between Tokyo and Osaka in one day (and is why the train was named Kodama, or ‘echo’).
“The ‘Kodama’ became so popular that tickets regularly sold out within ten minutes of being put on sale, one month in advance of the travel date.”