Maritime Communication


TECHNOLOGY – Learn about the technological advancements in maritime communication. There are three main reasons why ships need communication: navigation, coordinating ships or helping ships in need, and getting information.

Navigating or Way-finding

Until the discovery of radio waves, navigation was limited to only what could be seen or heard. Some examples of visual communication are a channel marker or floating buoys. The lighthouse increased the visual range beyond a vessel’s horizon limit of 7 to 10 miles. Built as early as 260 BC, the lighthouse at Alexandria shined 28 miles and signaled to seafarers to bring goods to the city to trade. Lighthouses also have sound signals like a bell, a horn, or a cannon fired at regular intervals to use during foggy conditions.

The Sabin Point Lighthouse, built in 1872 and destroyed in 1968. It was burned deliberately in July 1968 by the East Providence fire department in order to widen the shipping channel. From the Jess Welt Collection, SSHSA Archive.

Coordinate flotilla or help a vessel in need

Naval operations have always needed a form of communication between vessels. An Athenian fleet of triremes (Greek ships), in 480 BC set out to defeat the larger fleet of Persian vessels under the Emperor Xerxes. The Athenian Thermistocles controlled his flotilla of only 37 oar-driven Greek boats through a speaking trumpet and led the defeat of the 1200 ships of the Persian fleet. 

Speaking trumpets or megaphones are still in use today. Here it’s being used on the Steamboat Natchez in New Orleans, LA.

The age of sail used a speaking trumpet a great deal. Flag signals became the principal means of naval communications by the early 18th century. Flying the national ensign upside down is an internationally recognized distress signal. At night, flares can signal distress. A blue flare, which is often hand-held, signals that a vessel requests a pilot.

A diagram of the International Code Flags - provides the alphabet letter and meaning.
Diagram from “Flags, Funnels and Hull Colours” by Colin Stewart, SSHSA Research Library.

Seeking information, exchanges, or news and entertainment

 The telegraph used the Morse code to send messages. This code used long and short sounds that represent letters. Illustration courtesy of PBS Learning Media.

The telegraph’s invention marked the earliest and most effective method of communication at sea. As early as 1753, a Scottish writer discussed the concept. Britain’s William Sturgeon’s invention of the electromagnet in 1825 allowed for switchable high power pulses to be sent great distances on a single pair of wires. The patent award went to America’s Samuel Morse and Alfred Vail, whose design became the basis for all wired networks worldwide. They developed a system in 1836 of distinctive code using dots and dashes to represent numbers and letters. At sea, sailors used Morse Code with blinker lamps. A signaler operated a shutter at shorter or longer intervals to produce dots and dashes.

Elmo N. Pickerill is claimed to be the first to successfully use plane-to ground-to plane radiography. He went on to become the Chief Radio Officer on board the SS Leviathan and worked for RCA (the Radio Corporation of America).

The development of wireless telegraphy solved the problem of limitations in over-the-horizon communication at sea. Experiments in the 1830s discovered that electromagnetic waves might be generated. In 1862, Scotland’s James Clerk Maxwell demonstrated mathematically that these waves could be sent skyward and captured at a distance. His theory inspired new experiments that culminated in the work of Italian Guglielmo Marconi in the 1890s and made radio communication possible.

Additional Technological Advancements

This photograph shows Guglielmo Marconi (1874-1937) and his wireless telegraph. This invention came to be called a radio. The radio in the photograph included a 10-inch coil spark transmitter and a Morse linker. His early radios required large transmitters to send radio waves. Photo courtesy of PBS Learning Media.

England’s Frederick Guthrie developed the vacuum stem tube in 1873. America inventor Thomas Edison patented it in 1884, which led to innovations in electronics. For radio, it created the ability to transmit in continuous waves instead of pulses. Controlled frequency separation allowed for many stations to operate at the same time and created the ability to preform throughout the full radio frequency band. By continually altering transmitted carrier waves, voice and music can be sent over great distances. Called modulation, it  performs in several ways: Morse only requires an on/off switch; AM – or amplitude modulation – used for voice and music; and FM, or frequency modulation, allows for better reception of voice or music. Vacuum tubes did their job but were fragile and generated a lot of heat. It took many years before semi-conductor materials could be used.

In recent years, the development of pinpoint location for vessels at seas has revolutionized maritime communication. The Global Positioning System uses a network of 24 to 32 satellites orbiting 12,600 miles about Earth, with each circling the globe twice daily. Continuous ship-to-shore information can be sent by a ground station focusing on a satellite that relays data to the receiving sites.

Additional Resources

COHO Ferry blowing its Fog Horn while approaching Port Angeles, WA.

Tony Long, “Aug. 23, 1899: First Ship-to-Shore Signal to a U.S. Station,” Wired, August 23, 2011.

History of Marine Radio,” Arlo Maritime.

The Sea and Early Electrical Technology,” Engineering and Technology History Wiki.

Wireless Telegraphy,” Engineering and Technology History Wiki.

Neal McEwen, K5RW,  “‘SOS,’ ‘CQD’ and the History of Maritime Distress Calls,” The Telegraph Office Magazine (volume II, issue I).

D. Kenneth Richardson, “Historic Advances in Maritime Communication,” San Francisco Maritime Sea Letter (Spring/Summer 2018, no. 76).

Questions for Further Thought

  1. How does long-distance communication work? How did it improve communications at sea?
  2. Why did certain technologies fall out of favor? Explain the pros and cons of each method of communication.

Education Standards

National Standards for History

4.7A.6 Describe significant historical achievements of various cultures of the world.
4.8A.6 Identify and describe the significant achievements of important scientists and inventors. 
4.8C.4 Compare and contrast various systems of long-distance communication, including runners, the “talking drums” of Africa, smoke signals of Native Americans, the pony express, the telegraph, telephones, and satellite systems of worldwide communication today, and analyze their effects. 
4.8C.5 Identify and describe the people who have made significant contributions in the field of communication. 

Benchmarks for Science Literacy

8D/E2 Communication involves coding and decoding information. In any language, both the sender and receiver have to know the same code, which means that secret codes can be used to keep communication private.
8D/P1 Information can be sent and received in many different ways. Some allow answering back and some do not. Each way has advantages and disadvantages.