[2] The third part of the triangle was the line between Tonbridge and Hastings which had opened as far as Tunbridge Wells on 24 November 1846, Robertsbridge on 1 September 1851, Battle on 1 January 1852 and to St Leonards on 1 February 1852, running powers over the London, Brighton and South Coast Railway's line to Hastings having been negotiated.

[2] The Ashford–Hastings line had originally been promoted to run via Headcorn and Tenterden, but the government preferred the more southerly route.

The section from Headcorn to Appledore was authorised in 1892, and agreement was reached in 1896 with the South Eastern Railway over the operation of the line.

In 1898, the proposal was abandoned in favour of extending the Cranbrook and Paddock Wood railway to Tenterden and Appledore.

The Light Railways Act 1896 allowed for cheaper construction methods in return for a speed restriction.

A proposal was promoted in 1900 to build a line from Robertsbridge to Pevensey, which was to be worked by the Rother Valley Railway.

The South Eastern and Chatham Railway agreed to make up any operating losses in exchange for an option to purchase the line at any time within the next 21 years from the date of opening.

Headcorn was remodelled by the Southern Railway in 1930 to provide two through roads and the junction was then moved to the Tonbridge side of the station.

Correspondence with the Southern Railway in 1930 led to Sir Herbert Walker stating that there was no chance of the line making a profit, and that even if passenger services were withdrawn, it was doubtful whether the receipts from freight traffic would cover operating expenses.

He entered into negotiations with the Southern Railway aimed at disposing of worn out stock and obtaining serviceable replacements.

[7] When World War II broke out in 1939, the K&ESR again came under government control, being placed under the Railway Operating Division of the Royal Engineers.

A proposal to double the line wasn't carried out, but the track was again relaid to a higher standard, using rails salvaged from the Elham Valley Railway.

The final passenger train over the line before closure was a Locomotive Club of Great Britain railtour on 11 June 1961.

The line closed the following day, apart from a short stretch at Robertsbridge serving Hodson's Flour Mill, which became a private siding.

The Southern Railway refused permission for some of the K&ESR carriages to be taken to Lydd in 1947 citing safety reasons.

The preserved railway has had a tempestuous history, with two financial crises and disputes between the volunteer group and their elected board of trustees.

In the late 1990s, the company was almost bankrupted but avoided administration due to an error in the bank's loan agreement.

As with most heritage railways, the line has a number of paid employees to secure its continued operation and stages a variety of special events days to boost income.

It offers an 11+1⁄2 miles (18.5 km) ride through the Rother Valley in vintage and British Railways coaches usually hauled by a steam locomotive, although some off-peak services are operated by a diesel multiple unit.

Tenterden Town station is the main headquarters for the heritage railway, where a book and gift shop can be found, selling Thomas the Tank Engine gifts, the carriage and wagon department and a cafe that was once the Maidstone & District Motor Services bus station building from Maidstone, Kent.

Some are connected with local history and the railway whilst, as on other heritage lines, Thomas and Santa specials provide a commercial underpinning to the company's activities.

This houses a number of exhibits including a wax dummy of the colonel, telling the story of the man himself and of his railways.

This is a popular exhibit amongst children visiting the museum, many of whom delight in the collection of old railway magazines and timetables.

It aims to restore track and services east from the main line railway station to Bodiam.

The initial plan was to work towards operating brake van rides on the site, but progress was slow due mainly to lack of funds.

However, in 2011 this plan was dropped in favour of moving directly to a final layout suitable to handle the eventual traffic to and from Tenterden, with no interim railway operations.

Two landowners remain resistant to selling the necessary agricultural land for railway development, and the plans for a level crossing on the A21 in particular has caused local controversy.

On 16 March 2017, Rother District Council granted planning permission for the reinstatement of the line between Northbridge Street and Junction Road.

An application has been made for a Transport and Works Act order which would give statutory powers to rebuild and operate the line.

[37] The Kent & East Sussex Railway is the subject of the poem Farmer's Train[38] by Hugh Bevan,[39] illustrated by Rowland Emett,[37] and published in Punch issue dated 3 June 1946.