Research Collections Team

Signals at Sea

Flag signalling

Prior to the 17th century, the general way of communication was through word of mouth. The usual way for an Admiral to communicate with the captains of the ships in his fleet was to call them aboard his flagship. A banner of council was used to indicate this to his captains. There were certain internationally understood conventions: a yellow flag indicated sickness and quaratine, a red or "bloody" flag was a sign of battle and a white flag signalled a truce. When a ship surrendered, its flag was hauled down, and when the enemy has taken possession, the captor hoisted his ensign. It was legitimate to hoist false colours in time of war to confuse or entice the enemy within reach, but it was not allowed to engage or commit any hostile act whilst under false colours.

The first record of a system of communication between ships using flags, in the British navy is in 1653; the Instructions for the better ordering of the fleet in fighting, issued by Robert Blake, Richard Deane and George Monck. This system of flag signalling only used the ensign (white flag), union jack, a red flag, a blue flag and a pennant (a narrow tapering flag). An Admiral could convey various orders to his fleet by hoisting the flags in different positions. The problem was, that with so few flags, the signals were extremely limited. By the end of the seventeenth century, Admiral Russell introduced five more flags: white, yellow, striped red and white, striped red, white and blue, and the Genoese ensign (a red St. George’s cross on a white background). With a variation of hoisting along with the firing of a particular number of guns, it was now possible to make twenty-one maneouvring signals for the purposes of battle tactics.

During the eighteenth century, the number of signals that could be made by flags increased, partly by adding parti-coloured flags and early in the century, a code of signals was introduced. These were the first signals which to compass directions. Between 1740-1782, many signals were had been added, that by 1785, a total of fifty seven signals could be made. During the War of American Independence (1775-82), officers, such as Sir John Knowles, Richard Kempenfelt, and Lord Howe investigated the problem of further increasing the scope of flag signalling. The solution they arrived at was to use a numbered code. In 1790, Howe issued a new signal book in which this numerary system was adopted. Ten basic numeral flags, numbered from 0-9, were used singularly or in combination, being read from the top down, and had the same meaning wherever they were hoisted. The flag number could then be looked up in the new signal book and the number interpreted into a certain instruction or order. Howe’s numerary system became widely accepted. The number modifications to the flags during the Revolutionary Wars with France led to the Admiralty issuing the Signal book for the ships of war, in 1799.

Although this system provided a wider range of signals than ever before, signals were still limited to those listed in the book. However in 1803, the 1799 book fell into enemy hands and the Admiralty had to rearrange the signalling system to restore the security of ship to ship signals. In 1800, Sir Home Popham had devised a new signalling system, and his expanded version of the old system was introduced in 1803 to replace the lost 1799 code. Popham's system added twenty-five flags to represent the letters of the alphabet, so that any message not listed in the Signal Book could be spelt out, letter by letter, using the relevant flags. The most famous example of this was Nelson’s "England expects" signal at the battle of Trafalgar where ‘duty’ had to be spelt using Popham’s additional flags.

By 1813, Popham had found that the commonly used ten numeric flags were limiting and to spell additional words letter by letter made rather long signals. To combat this, he devised a system where alphabetic flags were hoisted in combination with the numbered flags to represent a code which was deciphered through the use of a kind of dictionary called Telegraphic signals or marine vocabulary. An example of the system is as follows: flags A.8.9 means ‘the enemy’, and flags 5.A.8 means "approaching". These flags hoisted in combination meant ‘the enemy is approaching’. This system allowed 11,000 three flag signals to be made and more if four flags were used. Popham’s vocabulary system was issued to the Navy in 1813 and from this time, vocabulary signals were used as part of the official flag signalling code of the Royal Navy.

There were also night and fog signals. From the 18th century to the middle of the 19th century, night signals were sent using four or fewer lanterns, placed in vertical or horizontal lines or in squares or triangles. Signals in fog could only be sent using gunfire. The number of firings and the timing of them provided different meanings.

Telegraph or Semaphore

Communications from the Admiralty to ships in one of the home ports had for centuries been sent by stagecoach or horse for centuries, and via despatch vessels if the ship was at sea. This was a slow process, and could take weeks, and sometimes months if it needed to get to ships at sea or on a foreign station. There was no way of giving instant advice or orders even in time of war. During the eighteenth century, people began to try to solve the problem of long distance signalling. It was not until the Napoleonic wars that the Admiralty began to take interest. The French were the leaders in solving the problem, and set up a telegraph system, devised by Claude and Abbe Chappe, radiating from Paris for communication with the army. The French system comprised levered semaphore arms that were attached to a beam fixed onto masts or towers nine or ten miles apart. The beam and the arms could be moved using ropes, so that they gave enough positions to represent the alphabet and numbers, the problem with the system was that it was difficult to achieve accurate angles with the three moveable parts, and so interpreting the signals could be difficult.

In Britain at this time, the navy had signal towers around the coast from Sheerness to Lands End. These could only set signals by using a combination of ball flags. These sent messages across land rather than from ship to ship. In 1795, Reverend John Gamble invented the shutter telegraph, which was a vertical board with five shutters mounted vertically, that could be opened and closed, giving thirty-one different signs. He was sent to Portsdown Hill for trials that were successful. However, when he arrived back at the Admiralty, he found that Lord George Murray had come up with the same idea, but with an improved shutter system to Gamble's. It had six shutters in two columns, giving sixty-three possible signs. The Admiralty Lords preferred this design, and after successful trials on Wimbledon Common in September 1795, Murray’s system was used. By the end of January 1796, fifteen stations up to eight miles apart had been built between the Admiralty in London and Deal, Chatham and Sheerness. Messages from Dover via Deal were said to have reached London in seven minutes. The Portsmouth line was the next to be completed in August 1796, and consisted of ten stations. Signals from Torbay and Plymouth were reported along the old coastal signal stations, and then telegraphed up the line from Portsmouth to the Admiralty. In 1805, the Admiralty decided to set up a line to Plymouth, branching off from Portsmouth, and had twenty-two stations. The line was completed by July 1806. It was recorded that a message from the Admiralty took three minutes to get to Plymouth and be acknowledged by return - a round trip of four hundred miles. In 1808, a line to Yarmouth was opened. The shutter lines were always considered a temporary wartime system and in 1814, the Admiralty closed the Yarmouth line and sold the eight stations on that line for £817. By the end of September, the coastal signal stations and the other shutter lines were closed for reasons of economy.

In 1815, when Napoleon escaped from Elba, and the coastal stations were reopened, though this time using a three-arm semaphore based on the French system. The Admiralty now decided that a permanent system using semaphore rather than shutters should be set up. In 1820, the experimental Chatham line was made permanent and extended to Deal and Dover. In 1822, the Portsmouth line was restored, and in 1826, the Plymouth line was begun. However, it was not completed since the electric telegraph was invented and replaced the semaphore system on land. The old shutter sites proved unsuitable for this new form of semaphore, so new buildings were built. In 1838, Wheatstone transmitted electrical signals between London and Birmingham. The Admiralty became interested, and by 1844 had signed a contract with Wheatstone and the London and South Western Railway Company to install and maintain an electric telegraph line between London and Gosport. Wires were laid following the railway tracks to the Royal Clarence Victualling Yard, Gosport, and then by submarine cable under Portsmouth Harbour to King’s Stairs in Portsmouth Dockyard. In 1847 the electric line was extended, and at the end of the year the semaphore system was made redundant.

From 1866 sea-going semaphore was derived from modifying the three arm shutter system for use with two arms. This system could then be used with hand flags instead of mechanical levers, and proved the fastest form of ship to ship signalling within its limited range. In 1867, Captain Philip Colomb decided that Samuel Morse’s code of dots and dashes to send messages could be translated to the flashes of a lantern. This could then be used for sending signals from ship to ship during the night, with short and long flashes of the lantern representing the dots and dashes of the Morse code. This method was adopted by the Royal Navy and greatly improved night signalling.

© Royal Naval Museum Library, revised 2002
The information contained in this fact sheet is correct as far as we are able to ascertain from our sources. It is not intended to be an exhaustive or complete history of the subject. Please contact the library for a bibliography of further reading materials, if available.

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Created on the 19 March 2003
Last modified on the 19 December 2003