The railway was supplied with three locomotives for the opening, built by Sharp, Stewart and Company. They had a 2-4-0 wheel arrangement, and the design was similar to others that the company had supplied for light passenger work. Sharp Stewart also supplied some rolling stock, and accepted debentures in part payment, only receiving one third of the total cost in cash. The six coaches, from the Bristol Wagon Works Co. Ltd., were very unusual, based on Cleminson’s patent flexible six-wheeled underframe, and having longitudinal seats and balconies (later enclosed). All platforms were on the south side of the line, so that (as with the Talyllyn Railway) doors were only provided on that side on passenger stock. The Midland Railway Carriage and Wagon Co provided the freight stock, including Cleminson 6-wheeled open wagons: this design was even used by the MOY Coal Co. for their unique private owner coal wagons.
Construction of the railway had cost £90,000, (equivalent to £8,400,000 in 2016), and the company applied to the Board of Trade for authority to raise more capital in 1880. Income from the operation of the trains did not produce enough surplus to keep paying the debenture interest, and in 1883 Sharp Stewart cancelled their arrangement, repossessing locomotive No. 1. The other two locomotives and the rest of the stock were then hired at £150 per year. In 1888, the company was authorised to raise another £10,000 in debentures, which was used to pay the arrears in interest on the existing debentures, and in 1890 enabled them to purchase the stock outright.
In the first month of operation, the company applied to the Board of Trade for permission to run the line as a light railway and this was granted on 11 March 1880. A maximum speed of 16 miles per hour (26 km/h) was specified, and it was to be worked by one engine in steam. Operation of the swing bridge (which was opened and closed by hand) was achieved using an Annett’s key, which was attached to the staff, which the working engine was required to carry. Passenger traffic for the first ten years was fairly static, at around 76,000 journeys per year, but goods traffic doubled to reach 9,000 tons. The next ten years saw a steady increase, with passenger journeys rising to 100,000 by 1900, while 9,000 tons of minerals and 6,000 tons of parcels were carried. In order to cope with the increase, another locomotive was ordered from Sharp Stewart in 1893. It was of a similar design to the originals, but slightly longer, and with a 2-4-2 wheel arrangement, providing a more-accessible coal bunker, and reducing the uncomfortable “boxing” (side-to-side motion) experienced with the 2-4-0s, particularly when running in reverse. It carried the name “Southwold” and the number 1, as its predecessor had done.