The most notorious local accident happened on Monday 3 October 1904. The train was a London express due to leave Llanelli at 13:05. The train consisted of 8 coaches and a six-wheeled van at the rear. The express engine was an “Atbara” class 4-4-0 No. 3460 Montreal. The train was to be assisted up the bank to Cockett by a 0-6-0ST No. 1674. This was common practice.
The train set off about six minutes late. On level track as it neared Loughor the tank engine derailed and was pushed over by the main line engine. Although the train was travelling at only 20 - 25 miles an hour the saddle tank rolled over as Montreal pushed passed and the first two coaches were badly smashed. Other coaches were also damaged.
The driver of the banker, John Lloyd of Delabeche Street, and a passenger, Mr O Stallard of Bristol, died at the scene. The fireman of the banker, Owen John Harries of Tinworks Row, and two passengers, Mr J Thomas of St Clears and Mr I Bryant from Somerset, died in the days that followed.
The investigation into the accident concluded that the saddle tank was not best suited for working ahead of a heavy train and had derailed because it rocked from side to side having of the high centre of gravity. The GWR used this arrangement all over its system every day and did not agree with the findings. However, it did place a speed restriction on trains banked this way.
A possible additional contributory factor was that saddle tanks were subject to surging water in the tank when part filled which could have increased the side to side motion.
The GWR gangs set about clearing the line and one track was reopened the following afternoon. In the meantime the GWR trains ran to Swansea via Pontardulais.