 Several upgrades and alterations to the Wairarapa Line have been made, but only the Western Hutt and Rimutaka tunnel deviations have significantly altered its route.In 1925, construction began on what was then known as the Hutt Valley Branch, leaving the main line just north of Petone station and running east to Waterloo, opening on 26 May 1927.After World War II, new state housing suburbs developed north of Waterloo, and the railway was extended to serve them.