Which railway began operating electric trains in 1890 as the world’s first deep-level underground railway?

The City and South London Railway began operating electric trains in 1890 as the world’s first deep-level underground railway. It initially ran between Stockwell and King William Street in London.

Unlike London’s earlier Metropolitan and District lines, which were built close to the surface and used steam locomotives, the City and South London Railway was bored through deep clay using tunnelling shields. Electric traction avoided smoke and fumes in the confined tunnels.

The original railway used small trains and narrow platforms. Its success demonstrated that deep tunnels could carry frequent urban passenger services beneath crowded streets.

The line later expanded and became part of the London Underground network. King William Street was eventually replaced by a new alignment, so some features of the original route no longer survive in regular service. The railway is an important ancestor of the modern Northern line.