Signalling Part 1

Communication between ships at sea has always been difficult. Unlike on land, sending a messenger is not usually very practical, so navies from the very earliest days have had to come up with other methods of passing messages.

The Battle of Salamis

The first recorded naval signal came during the Battle of Salamis, when an oar with a red flag attached was raised from the Greek flagship as a signal to stop luring the Persians deeper and instead launch the attack, which ultimately scattered the Persians and turned back Xerxes' invasion of Greece.¹ And this set the pattern for operational signals for most of the next two millennia. The commander of a fleet would set up specific signals to support his plan, maybe declaring that a blue flag meant "attack the enemy" while a red flag meant "withdraw". Over time, some of these signals became traditional, and certain banners would be flown when a ship sighted the enemy, or when an admiral wanted his captains to come to the flagship for a conference. Sails were often used for signals, too, with the flagship letting fly the fore topsail being the traditional signal for the fleet to prepare to get underway.

A sailor fires a flare to signal at night

Of course, flags didn't work in all circumstances, particularly when the visibility was bad, at night or in fog. Guns, presumably firing blank charges, were commonly used for signalling in these conditions, although the vocabulary available was even more limited. Only simple signals, like "I have spotted the enemy" and "I am in trouble" could be sent. Lights could also be used at night, although they were only used in straightforward ways, like the ship nearest an enemy in pursuit showing a light in the stern to guide the rest of the fleet. Some of this was because the tactics of the day were very simple, and didn't require complicated signals to support them.²

Blake's flagship signalling in battle

In many ways, tactics and signalling evolved alongside each other, particularly as the line of battle developed under Robert Blake and his successors. Blake gave orders by hoisting five different flags from five different points on his ship, producing a total of 25 possible signals. Later, after the restoration of the monarchy, the future James II as Lord High Admiral took an interest in matters of signal, publishing the first signal book in 1673. However, over the next century, the number of required signals grew with the complexity of naval tactics, and by 1780, there were 50 flags in use for 330 signals. Worse, the flags were poorly designed, and it was often hard to tell the difference between them, particularly in poor lighting conditions.

Sir Home Riggs Popham

But help was at hand. Richard Howe, a British Admiral, had devised a new signal book in 1776, making use of only 21 flags, with each flag assigned a specific number. This meant that the flags could be carefully designed to make them easy to distinguish. Combinations of flags, known as hoists, were flown to indicate a page in the signal book and a specific signal on that page. However, there was still no real standardization, and each admiral provided his own signal code, which obviously caused great potential for confusion. This bizarre practice lasted until 1799, when the Admiralty finally intervened, adopting a standard signal code. This didn't stop private development of signals, and Captain Home Popham came up with an excellent elaboration on the previous codes, allowing about 30,000 words in 3 and 4-flag hoists, as well as assigning each flag a letter in case more words needed to be spelled. This was enough to give room for some rather unusual signals. Examples given in his code include "YOUR SISTER MARRIED TO A LORD OF THE ADMIRALTY" and "A CHANGE OF MINISTERS IS ABOUT TO TAKE PLACE". His system was the one in use at Trafalgar, when Nelson gave the famous signal ENGLAND EXPECTS THAT EVERY MAN WILL DO HIS DUTY.³

Victory flying ENGLAND EXPECTS THAT EVERY MAN WILL DO HIS DUTY

Flag signalling was not the only form of communications that Home Popham worked on, either. During the Napoleonic Wars, the French invented the semaphore telegraph, a system for very quickly relaying messages between stations on land. The Admiralty adopted a similar system, developed by Bishop George Murray, to transmit messages between the Admiralty and the major fleet bases. Each station consisted of six shutters that could be rotated to the horizontal or vertical position, allowing 64 different combinations. This system passed a message over the 69 miles from London to Deal in Kent in just 60 seconds. With the end of the Napoleonic Wars, the Admiralty sought a better system, and selected the one devised by Popham, which consisted of a tall pole with two rotating arms, one at the top and one in the middle. His system remained in service until 1847, when the electric telegraph replaced it.

One of Murray's semaphore stations

While it was obviously impossible to construct long chains of semaphore stations at sea, the basic idea behind it was soon adapted into what most people think of when they hear the word semaphore, flag semaphore. This involved the use of two flags, with each letter and number assigned a certain position, allowing complicated messages to be passed much faster than was possible using flag hoists. This largely replaced the previous practice of passing detailed messages by coming close alongside another ship and shouting through speaking trumpets, except at night or when dealing with merchant ships, and was important enough that many warships of the late 19th century were fitted with mechanical semaphores in addition to hand-held semaphore flags, although even these still had a limited range. The end of that century saw the signal lamp become common, allowing the signalmen to pass information over even longer distances using Morse Code. These were bright enough to work reasonably well even in the daytime, and remain in limited use today because they allow communication even when ships are operating under radio silence. However, these systems still had limited range and generally were directed to a specific recipient, so flags remained in use to pass orders to the fleet as a whole.

A signalman aboard New Jersey uses semaphore to pass a message

So how did that process actually work? Let's say that an Admiral wanted to order his fleet onto a new course. He would give that order to his Flag Lieutenant, a junior officer who was in charge of his signal section.⁴ The flag lieutenant would find the appropriate signal in the book, and give orders to the signalmen⁵ to prepare the appropriate flags. They would get the flags out of the locker and attach them to the signal halyard, often set up so they could be hoisted folded and then broken to full visibility. The signalmen on the receiving ships would decipher the order from the flagship, then run up the same flags to signal receipt and give the flagship the chance to confirm that it had been received correctly. Finally, when the Admiral gave the order to execute, the flagship's hoist would be hauled down, synchronizing the maneuver throughout the fleet.⁶

An Iowa signalman passes a message using the signal lamp

Today, flag signalling has been largely superseded by radio in various forms, but it has remained in a few niches, when messages need to be longer-lasting that the instant transmission of radio. Flags are often flown with ship's radio callsigns, and for short messages, like Bravo Zulu, which means "Well Done". They are also used to indicate a vessel's status. For instance, the Bravo flag is flown by ships loading or unloading ammunition, while the Q (Quebec) flag is a request to the local authorities to certify the vessel as disease-free and allow it to dock. A Delta Flag indicates that the ship is having difficulty maneuvering, and that other vessels should stay away.

Flags are run up aboard Iowa in the 1980s

Despite the development of flags, and the skill of the crews in their use, something better was coming. Starting from the mid-1890s, radio went to sea, and would revolutionize everything.