In the earliest days of railways, and before the electric telegraph had been developed sufficiently to allow reliable communication along the length of the line, control by timetable and time-interval dispatch was the only available method. The early passenger main lines were built as double lines but it soon became obvious that intermediate checks on the running of the trains were needed, and so each running line was divided into ‘blocks’ with a man guarding the entrance to each block. These men were called policemen and organised like their civil counterparts. In this sys¬tem the policeman allowed a train to go forward into the next block after a predetermined time interval had elapsed. As the policemen could not communicate with one another, except by messages carried by the trains, it was possible for dan¬ger to arise if a train failed somewhere in a block out of sight of the policeman controlling entry to it.

So long as the rules were obeyed this was a safe enough system for the traffic of its day, but it could not cope when traffic density became high. Thus the first permanent signals appeared at junctions in 1841 and interlocking of points with signals in 1860. Crude forms of the electric telegraph also appeared in 1841 and by 1855 the South Eastern was using it to work the line to Dover by the block system. Intervals of space now separated successive trains, but it was not until the Regulation of Railways Act of 1889 that the block system was made compulsory and all main lines were so worked. The duties of the ‘policemen’ were now becoming confined to the operation of signals and points and they were renamed signalmen, though in some areas they are still nick-named ‘bobbies’.

However, the actual signalling equipment tended to retain the character of the individual companies as they either continued to produce their own equipment or to purchase it from a specialist supplier. The early signals were semaphore, which was satisfactory as long as train operation was confined to daylight hours. However, the demand for evening and night time operation, during times of restricted visibility (fog), and operation in tunnels required lights. Semaphore signals had lights attached to them and various schemes were employed whereby lights of different colours were displayed depending on the setting of the semaphore arm.

This situation lasted through the grouping era and well into BR days. Signals were long-lived, and it was common for signals installed by the pre-group companies to remain functional until replaced by colour lights. Colour light signals first appeared about the end of the 19th century. They were known as tube or tunnel signals and were used where a semaphore arm would be invisible or the clearances would be very small. Comprehensive colour light schemes were installed on some heavily used commuter lines into cities in the 1920s. Long stretches of the East Coast Main Line were equipped by 1940, and this gradually spread to other main lines. Conversion was a slow process, and it was only by 1990 that all of the principal main lines were controlled by colour light signals. Even at that time many miles of secondary and less heavily used main lines remained under semaphores.

Modellers should be aware that there were considerable geographical and historical variations in signalling equipment and practices. If modelling a particular railway at a particular date in history, research will be necessary to establish the particular characteristics of the signals. A list of further reading is available. Heritage railways often continue to employ original or refurbished signalling equipment and communication practices, and may also be a useful source of information.

An early version of this article appeared in the Gauge O Guild Manual. It was adapted and developed for the GOGWiki by Nick Baines.