Ever since the invention of the steam locomotive, trains have played a vital role in the mobility of armies. The Second World War was no exception. As well as transporting troops and supplies, however, trains performed another function. They became mobile gun platforms, more heavily armed and armoured and faster than tanks.
Thus it was that when Britain was threatened with invasion in 1940, the War Office sanctioned the creation of several armoured trains, each allocated an identification letter, between A and M. These trains were given particular areas of railway line to patrol, covering areas such as that between the Tyne and Tweed, Lincolnshire and Yorkshire. A number of trains covered areas in Scotland, armoured train J, for example, being responsible for patrolling the Kingdom of Fife. Armoured train K is, however, of particular interest here since it covered the area between Edinburgh and Berwick-upon-Tweed.
Armoured train K, powered by a single locomotive, No 7573, was armed with two 6-pounder guns, as well as six Bren machine guns, two Vickers machine guns, four Thompson sub-machine guns (Tommy guns) and numerous rifles carried by the crew. All in all, this was an impressive array of weaponry at a time when the most heavily armed British tank, the Infantry Tank Mk II Matilda, mounted only a single 2-pounder gun and one 0.303 Vickers machine gun.
A number of different routes were authorised for armoured train K to patrol, although generally it was restricted to short patrols, largely because of the vital need to keep the east coast main line free for normal traffic. However, the 12th Armoured Train Detachment of the Royal Engineers, the unit which operated armoured train K, was given permission to patrol a number of branch lines, including West Calder, Linlithgow, Inverkeithing, the Waverley Line to St Boswells, Peebles as well as Gullane and North Berwick. Patrols were carried out weekly.
The train was initially based at St Margaret's depot in Edinburgh, but this was interfering with railway operations and it became necessary to find alternative accommodation. Train K then moved to Longniddry, from which it could easily patrol the coastal branch lines in East Lothian. However, the only accommodation in Longniddry for the train crew was in the golf clubhouse, which proved quite unsuitable, and within a month another move was made to North Berwick. The train itself, however remained based at Longniddry and a bus was provided to shuttle the crew from the railway depot at Longniddry to their billets in North Berwick.
In 1942 Scottish Command decided to transfer the operation of its armoured trains to the Home Guard. As a result, it was felt necessary to reorganise which depot the trains were based at. Armoured train K was trans-ferred to Saughton Junction, with orders to transfer to Drem upon receipt of the order 'Action Stations'. On 6 June 1942 armoured train K was transferred from its Polish crew to the 10th City of Edinburgh (4th LNER) Battalion, Home Guard.
As the threat of invasion receded, the armoured trains were withdrawn from service in England. However, Scottish Command argued that the trains were of importance to the defence of coastal areas in Scotland and also that the crews of the trains were keen and demonstrated considerable interest in their work. As a result, the three armoured trains in Scotland remained, although a decision from Whitehall regarding non-standard weapons on the trains resulted in the Tommy guns being removed from service.
In early September 1944 LNER informed the War Office that locomotive No 7573, which powered armoured train K, was due for its five-yearly boiler examination, and requested its release to Stratford for this reason. Although there were sufficient engines to maintain the three armoured trains, it did raise the question again of whether they continued to be of any useful purpose. By that stage of the war, there was clearly little threat of an invasion of Scotland and the decision was taken to withdraw the armoured trains from service. The Railway Executive Committee was informed by the War Office of this decision on 5 November 1944.