The South Wales Railway () was a main line railway which opened in stages from 1850, connecting the Great Western Railway from Gloucester to South Wales. It was constructed on the broad gauge. An original aspiration was to reach Fishguard to engender an Irish ferry transit and transatlantic trade, but the latter did not materialise for many years, and never became an important sector of the business. Neyland was the western terminus of the line until 1906.

The company amalgamated with the Great Western Railway in 1863 and the track was converted to narrow (standard) gauge in 1873. In 1922–1923, most of the independent Welsh railways were constituents of the new enlarged Great Western Railway, enabling rationalisation and benefits of scale. Nearly all of the original main line of the South Wales Railway remains in use at present (2020).

Proposals

The prospectus of the South Wales Railway was issued in the summer of 1844. It proposed a railway with capital of £2,500,000 to run from Standish, on the Cheltenham branch of the Great Western Railway where the Bristol and Gloucester line joins it. Over the River Severn at Hock Cliffe between Fretherne and Awre and then follow the coast to Chepstow, Newport, Cardiff, Bridgend, Aberavon, Neath, Swansea, Carmarthen and Fishguard, with a branch line from near Whitland to Pembroke Dock.

The prospectus was published widely as a newspaper advertisement: Surveys have been made of the line of country best adapted for accommodating the extensive traffic of the great mineral basin of South Wales, and the important agricultural interests of that country, as well as the intercourse between the ports of Cork, Waterford, Wicklow, Limerick and Wexford, the inland and manufacturing districts of England and the metropolis.E T MacDermot, History of the Western Railway, volume I part II, published by the Great Western Railway, London, 1927

The line was to pass "within an easy distance of Monmouth" and west of Carmarthen, it was proposed

"that the railway shall divide into two branches, one to the naval arsenal of Pembroke and the harbour of Milford Haven Waterway, and the other to Fishguard, whence a communication with the South of Ireland would be effected within six hours."Prospectus in the Monmouthshire Merlin, 15 June 1844, accessible at the British Newspaper Archive, subscription required

Chief among the objectives of the line was communication with Ireland; the engineer was Isambard Kingdom Brunel. The project was sponsored by the Great Western Railway and in February 1845 the GWR announced that they had promised £500,000 towards the formation of the company. It was to be "a great national undertaking to connect the South of Ireland as well as South Wales with the Metropolis".

The people of Monmouth were disappointed that the line was not to pass through their town, and they urged a deviation to run through Gloucester, Monmouth and Usk to Caerleon, adding 18 miles to the route and involving considerably worse gradients. The Admiralty objected to the Severn bridge, and the result was that the line was authorised west of Chepstow only, with a branch to Monmouth. The line was to be broad gauge, although this was not explicitly defined in the (8 & 9 Vict. c. cxc).

In the 1846 session of Parliament, a revised bridge crossing of the Severn at Fretherne was proposed, and alternatively a tunnel. Both options were rejected in Parliament, and the company was obliged to concede the longer route through Gloucester, crossing the Severn there.

A local railway thus became of strategic importance: the Gloucester and Dean Forest Railway had been authorised in 1845 to connect with the Monmouth and Hereford Railway near Grange Court. If the Gloucester and Dean Forest Railway extended southwards to Hagloe Farm, two miles south of Awre, the South Wales Railway could connect there. The arrangement was approved and both companies got their acts of Parliament, the Gloucester and Dean Forest Railway Act 1846 (9 & 10 Vict. c. ccxl) and the South Wales Railway Amendment Act 1846 (9 & 10 Vict. c. ccxxxix) respectively. Soon after gaining royal assent the GWR agreed with the G&DFR that the former would take over the construction and build the line themselves.Rex Christiansen, A Regional History of the Railways of Great Britain: Volume 13: Thames and Severn, David and Charles, Newton Abbot, 1981,

The (9 & 10 Vict. c. ccxxxix) also authorised a branch from Landore to Swansea, as the original route had not been intended to enter the town centre,Swansea gained city status in 1969. and another from a point near the later Clarbeston Road station to Haverfordwest.

Soon after the passing of the act of Parliament the company agreed with the Gloucester and Dean Forest Railway that the SWR would build the southward extension itself, so that the northern limit of the SWR was to be at Grange Court, about 6 miles from Gloucester.

Agreement was reached with the Great Western Railway that the GWR would lease the SWR on completion of the line to Fishguard, paying 5% on the capital plus half of surplus profits.

The track gauge of the South Wales Railway A Gauge Commission had been established by Parliament to consider the desirability of a uniform track gauge for the railways of the United Kingdom, as the negative effect of the difference of gauge between contiguous railways was beginning to show.

The Great Western Railway and companies friendly to it used the broad gauge, while the narrow gauge (later known as standard gauge) was in use on most other lines. Where two lines of different gauges connected, goods and minerals making a through transit had to be physically transshipped, and passengers had to change trains.

The commissioners declared that the break of gauge was "a serious evil" and they recommended that no further railway should be constructed on the broad gauge system, though they hoped that "some equitable means should be found of producing such entire uniformity of gauge or of adopting such other course as would admit of the Narrow Gauge carriages passing, without interruption or danger, along the Broad Gauge Lines."Gauge Commissioners' Report, quoted in MacDermot, volume I part I, page 235

If implemented, this finding seemed to mean that the South Wales Railway could not be built on the broad gauge, introducing a break of gauge with the parent GWR at Gloucester or Grange Court.

The Lords of the Board of Trade considered the matter, and they modified the policy. It was their opinion that the SWR should be made on the broad gauge, and the resulting Railway Regulation (Gauge) Act 1846 (9 & 10 Vict. c. 57) stated that the railways authorised

Accordingly, the line was built on the broad gauge, with far-reaching consequences.D S M Barrie revised by Peter Baughan, A Regional History of the Railways of Great Britain: volume 12: South Wales, David St John Thomas, Nairn, 1994, E T MacDermot, History of the Great Western Railway: volume I part 1: 1833–1863, published by the Great Western Railway, London, 1927

There were prodigious engineering works to be undertaken: the crossing of the River Wye at Chepstow, a large timber viaduct at Newport and a tunnel there, a further large timber viaduct at Landore, and crossings of the River Loughor and River Towy further west. The depressed state of the money market immediately made the raising of subscriptions difficult, and the company suffered a major loss when the timber viaduct at Newport, almost completed, was burnt down on 31 May 1848, being completely destroyed. It had cost £20,000.

A key objective of the promoters of the line was to connect southern Ireland by ferry from Fishguard to a harbour near Wexford. It was hoped that the Post Office contract for the carriage of mails between London and Dublin could be secured for the Great Western Railway and its allies. In Ireland, the Waterford, Wexford, Wicklow and Dublin Railway Company was to handle the traffic. Brunel also hoped that a transatlantic shipping business using Fishguard might be developed.

However, in 1845 there was a catastrophic failure of the potato crop on which a majority of Irish people depended for a living; this resulted in mass starvation and commercial depression, which deepened the following year. The catastrophe is known as the Great Famine of Ireland. The economy in Ireland worsened considerably, at the same time as the general economic climate throughout the United Kingdom declined sharply.

On the Irish side the depression was so extreme that the railway partners considered that it was impossible to proceed with the construction of their railway. Fishguard at the time only had significance as a potential ferry port, and the building of the South Wales Railway to that point would obviously be wasted expenditure, so that the directors decided to cut it short. The GWR guarantee of 5% on capital was only to come into effect when Fishguard was reached by the SWR, so the latter's directors approached the GWR proposing that the guarantee should come into effect when the line reached Swansea instead. The GWR were not agreeable to this, leaving the South Wales Railway in a difficult position; certain persons who were directors of both companies saw that their positions were untenable, and resigned from the SWR, and the hitherto supportive relationship between the two companies now took a seriously unfriendly turn. It was stated that as the GWR had about a quarter of the SWR shareholding, they were being duplicitous in failing to support the abandonment of the Fishguard part of the line.

A committee of shareholders reported their view of the situation:

The Great Western Railway was accused of duplicity:

SWR directors who were also GWR directors had had an unhealthy influence on the affairs of the SWR:

First sections of line opened

Chepstow to Swansea The first portion of the line was opened on 18 June 1850, from Chepstow to Swansea. It consisted of 75 miles of double track, on the broad gauge, using Brunel's longitudinal timber track. Engines and rolling stock were provided by the Great Western Railway; they arrived by coastal shipping, as the line was not connected to any other line. Soon after the opening a slip in the deep cutting slope took place at Llansamlet, between Neath and Swansea. To stabilise it, Brunel erected the so-called flying arches, loaded with slag, to resist the thrust.

Brunel's most substantial timber work, not just on the SWR, but as far as his work was concerned for any railway company, was to be found in the vicinity of Swansea. Crossing the River Tawe and the Landore marshes, the Landore viaduct formed a continuous timber work, exactly one-third of a mile long, with thirty-seven spans ranging from 40 to 100 feet.

Construction was of course proceeding on the section between Landore and Haverfordwest, and between Chepstow and Grange Court. In November 1850, the work on the line towards Fishguard (west of the point of junction for the Haverfordwest branch) was resumed; it had been suspended since the autumn of 1848. The instruction to complete the line may have been in frustration at the GWR position on the lease agreement. Further negotiation took place and the agreement in March 1851 took the form that the GWR would lease the line for 999 years from the time of completion from Grange Court to Swansea. The GWR were to take one third of the net profit, but pay a rental on the line; the SWR would provide the staffing other than the locomotive department. The work of completing the western extremity of the line was again discontinued.

Gloucester to Chepstow Completion of the Chepstow bridge was much delayed, while the easier construction between its east side and Grange Court was proceeding well. Construction of the Gloucester and Forest of Dean Railway was also going well, although the opening bridge over the Severn at Gloucester, and the junction arrangements with the GWR at Gloucester station were causing delay.