On 23 March 1939 a trial run was made with a 4-6-0, with the locomotive and tender separated at Stranraer to turn them. "There was no prospect of the 60 ft turntable being ready before late summer, so they laid longer rails, projecting at each end, on the existing 50 ft turntable. This allowed them to turn a Class 5 4-6-0. The class 5s began to work from Glasgow to Stranraer on 16 April 1939. It was about October that the new 60 ft turntable was ready at Stranraer. Class 5X 4-6-0s were drafted in, and were the mainstay of the Stranraer road throughout the war. World War II brought exceptional amounts of traffic to the line. Smith records that 36 troop trains traversed the line in April 1940 as British forces were built up in Northern Ireland against the possibility of an enemy invasion of the Republic of Ireland. By the end of the year,  Large numbers of troops were now stationed in Northern Ireland, and the ordinary passenger [train] service proved quite inadequate for men going on leave to England and Wales. A special sailing had to be provided, with two large trains in connection. A train from London and one from Cardiff worked into Stranraer in the early morning, returning in the evening about 6.30 p.m. These were made up eventually to 16 coaches, each with a buffet car. Siding accommodation at Stranraer was terribly inadequate. They could service only one of those huge trains, so the Cardiff train had to be hauled to Ayr and back each day for servicing. Two Caley [Caledonian Railway] Class 3F 0-6-0s were put on this job. Later in the war it was decided that an emergency west coast port should be established, to continue transatlantic trade in the event that Glasgow or Liverpool docks were disabled by enemy action. A new harbour facility was developed on Loch Ryan, called Cairnryan Harbour, and it was served by the "Cairnryan Military Railway". This was a considerable undertaking. The new railway joined the Stranraer to Challoch line at Cairnryan Junction, about two miles (about 1 km) east of Stranraer, facing for trains approaching from the east. The point of junction was later moved closer to Stranraer, at Aird. The line opened in July 1942. In the event the port was not needed, and only eighteen fully laden ocean-going vessels used the port during its lifetime.