On the 2nd of July, 1938 the electrified train line between the Wellington Railway Station and Johnsonville was opened by Minister of Railways Dan Sullivan and Wellington Mayor Thomas Hislop. The line was originally built in 1886 as part of the main train line north out of Wellington. After the Tawa deviation was finished in 1937 the Johnsonville section was shortened and it was converted to a suburban route. New Electric trains built in England and New Zealand replaced the old steam engines for the route.
The electrified network would continue to expand during and after the Second World War.