Visual Signaling at Sea

Hello everyone! Welcome back to “Karl’s Korner”, a historical segment written by myself, Karl Zingheim - Ship Historian of the USS Midway Museum! The USS Midway Museum regularly employs colorful flags to convey simple messages to the world from either side of the carrier’s island superstructure. Today I will tell you what these flags means and how they are used for messaging and signals.

Visual Signaling

These flags each represent a letter or numeral which can be used to literally spell out words in a sentence, or, more often, they are employed in pre-arranged alpha-numeric sequences that can concisely represent more complex concepts that can be deciphered in a common codebook. Similarly, trained personnel can display hand-held flags and transmit messages through various arm postures in a method known as “semaphore.” Light can also be used to send information at sea, and naturally started with night signals, a method that survives today in the specialized navigation lights vessels employ after dark. The advent of electricity permitted the adoption of powerful signal lights that could be masked with shutter “blinkers” that controlled the emission of light, rendering the resulting flashes into a decipherable code pattern.

Though seemingly cumbersome and quaint, visual signaling offers an advantage over radio communications through its security. Since radio waves can travel great distances, they can be intercepted, and perhaps understood, by opponents. Furthermore, a radio signal, even if indecipherable, can be traced to reveal the location of the sender. Visual signals, however, require a line-of-sight connection between sender and receiver, often at distances that render the consequences of enemy interception moot. Therefore, they are useful in communicating within a formation of ships within visual range of one another, without running the risk of detection from without.

Visual signaling has been around at least as long as the necessity for ships to exchange information beyond voice hailing distance. In naval warfare during the age of fighting sail, specialized flags conferred messages for maneuvering lines of ships, as well as reconnaissance contacts. Indeed, a common ruse de guerre involved flying a national flag of a friendly or neutral state to create a false impression about one’s allegiance or intentions. A famous case occurred in World War II when the German auxiliary raider Kormorant deceived the Australian cruiser Sydney as to her identity and lured her into range of a powerful battery of hidden 6-inch guns and torpedoes.

Light, in the form of flames, was the fastest method to convey information. In 1588, when English coastwatchers in Cornwall discerned the massed sails of the Spanish Armada entering the English Channel, they ignited a series of bonfires along the shore, bringing news of the invading fleet’s arrival to London in a matter of minutes. Light signals could also be used against an enemy to confuse him or buy time. When a British commando force entered the German-occupied port of St. Nazaire in 1942, a signal light challenge from shore was returned rapidly, causing the defenders to ponder who was challenging whom, giving the attackers precious minutes to continue their advance towards their objective.

However, visual signaling can go awry. Because discerning a flag or light is critical to understanding a message, visibility restrictions can play havoc. A sender may be flying flags seen only from edge-on by the intended recipient, or smoke, haze, or intervening structures may block the line-of-sight. Attempting to convey more complex messages requires having a comprehensive signal book. An example of such a thing going wrong occurred during the Battle of Dogger Bank in 1915 when a force of British battlecruisers pursued their German counterparts across the North Sea. The British flagship, Lion, was disabled by shellfire and slowed, causing her to fall behind. The British commander, Admiral David Beatty, ordered a signal flown directing the rest of his force to continue the pursuit of the fleeing enemy. Instead, the resultant signal vaguely directed a concentration on the nearest enemy ship, a crippled cruiser at the end of the German column. As a result, the other British ships directed their fire on this unfortunate vessel, permitting the rest of the German squadron to escape.

Another drawback to visual signaling is its slow speed. Columns of warships can stretch beyond easy visual range of the lead ship, so a method of having each ship display the signaled order from the flagship arose to ensure that each ship understood what was going to happen. When the last ship in line repeated the flag signal correctly, the order would go into effect, or be “executed”, when the flagship hauled down the signal and the ships would conduct the ordered maneuver. This worked fine when ships were propelled by wind, but as the speed of powered vessels increased, the working time fell drastically. Admiral Beatty encountered this very problem at the Battle of Jutland in 1916 when his speeding battlecruisers, thundering ahead at 25 knots or better, took several minutes to repeat his maneuvering signals before they could be executed. This led to a near disaster for the British fleet when Beatty needed to come about when the main German fleet was spotted approaching. Although his immediate force of ships followed him around, he could not convey the need to alter course quickly enough for his Fifth Battle Squadron in the rear to comprehend and act. The result in this swiftly-moving action was the exposure of that force to the firepower of the German dreadnoughts for several minutes before they discerned Beatty’s intentions. Fortunately, the Fifth Battle Squadron comprised a new class of fast dreadnoughts with sufficient armor protection and speed to avoid catastrophic damage. After the war, Beatty reflected that his signals officer, “Cost me three battles.”

Finally, there is another realm of visual signaling in the Navy unique to carrier aviation. The flight deck is a noisy environment, and to direct alterations to the status of an aircraft, such as engine or flap settings, as well as to guide aircraft about the deck, flight deck directors, or “yellow shirts,” employ an array of hand signals to the pilot. Similarly, the Fresnel optical landing system on carriers is a high-tech extension of the visual signals the Landing Signal Officer used with is famous set of paddles. When an aircraft is ready to launch on the catapult, the catapult officer, or “shooter,” exchanges a simple hand salute with the pilot to send the plane down the track and aloft for its mission.

Thank you for reading the latest Karl’s Korner! Did you learn something new? Leave me a comment below and let me know what you learned – and be sure leave any other topics you’d like to know more about!

Launch em’… until next time,

Karl