The International Code of Signals (INTERCO) is a standardized system of communication used by seafarers worldwide to facilitate effective communication, regardless of language barriers. It employs a combination of flags, lights, and sound signals to convey important messages related to navigation, safety, and other operational matters, reports Marine Insight.
A Brief History
Before the International Code of Signals came into being, several naval and private signals were in use, such as the Marryat’s Code in the mid-1850s.
From the early to the mid-1800s, Britain, France and the United States undertook it upon themselves to devise their signaling systems and the British Royal Navy introduced a flag signaling method.
The British Board of Trade drafted the International Code of Signals in 1855, which was published as the Commercial Code in 1857. It offered common signals, mainly using flags for communicating messages like distress, navigation requests ,and vessel identification.
The need for this code was felt as maritime trade and shipping increased in the 19th century and earlier signaling was restricted to specific regions or nations leading to barriers in communication. With time, this code was revised and new methods of signaling like the use of Morse code were introduced.
After the Second World War, the IMO became active in standardizing maritime communication and so the code was further refined to incorporate modern maritime technologies like radio signals while the flag system was retained.
Today, the International Code of Signals is maintained by the IMO which published an edition in 2005. It includes visual signals or flags, sound signals like whistles or horns, and radio communication protocols. These signals are recognized universally by all maritime professionals.
Signals Used In INTERCO
Signals can be divided into three categories
- Single-letter signals that are important, urgent and common.
- Two-letter signals for other messages, followed by a numerical complement sometimes, to supplement the message.
- Three-letter signals starting with M which are Medical Signal Codes.
- Flag Signals (Using Specific Flags)
As the name suggests, flag signals use flags or pennants to convey important information. One or two flags were used to enable communication at a distance before the radio was invented. In Flag hoist signaling, each flag or a combination of flags has a preassigned meaning or code. The INTERCO has a standard set of flags and an associated alphabet for international use and also a set of codes.
Flag Signals are used for
- International distress signals, e.g. using a single flag representing an emergency.
- Giving navigational warnings like signaling a ship’s course or location.
- Sending Requests for Assistance, e.g. signalling for medical help or for towing a vessel
Every signal can be easily recognized from a distance as the flags are in bright colours and distinct patterns.
- Morse Code (Through radio or light signals)
A signal lamp also called a Morse lamp or Aldis lamp is a visual signalling device for communicating using flashes, typically using Morse Code. The concept of flashing dots and dashes from a lantern was envisaged by Captain Philip Howard Colomb of the Royal Navy in 1867, though his code was not the same as Morse Code.
In WWI, Germans made use of optical transmitters using Morse code within a range of five miles with red filters.
Today, signal lamps generate a focused pulse of light, by opening and closing shutters in front of the lamp or by using a concave mirror. They are still used on naval ships and in air traffic control towers, in case the radio communication fails.
- Flag Semaphore
Flag Semaphore is another effective system of communication when the two parties are at a distance from each other. It uses visual signals like flags held in both hands at different positions, disks, paddles, rods etc.
The semaphore system was greatly used in the 19th century and is still used today during underway replenishment at sea and for emergency communication in daylight or by using lighted wands rather than flags at nighttime.
- Sound Signals (Using a Ship’s horn or whistling)
Sound Signals, including the use of horns or whistles, come under the International Regulations for Preventing Collisions at Sea and may be used in situations when using flag signals is not possible. The use of sound signals is important to avoid ship collisions in bad weather or low visibility at sea and ensure safe navigation.
- Voice Communication (Through Radio)
Using voice communication via radio is the easiest way to communicate. Several standard maritime communication phrases can be used to convey the message to the crew members of the other ship. This method of communication is convenient and can be used when there is considerable distance between the two parties.
Components of the INTERCO System
The International Code of Signals uses a combination of signal flags, messages and alphabetic codes and has the below-mentioned components.
Alphabetical Code
Every letter of the alphabet is assigned a specific flag which is used individually or in combination to convey messages.
For instance, the flag for letter A is a white and blue flag with vertical stripes and B is a yellow and red flag with vertical stripes.
The 26 Nautical Flags beginning with a new alphabet represent a new message.
For example:
Alpha- “Diver down, keep clear.”
Bravo- ‘I am taking in, discharging, or carrying dangerous goods. ‘
Charlie- “Yes” (confirmation).
Whiskey- ‘I require medical assistance. ‘
Message Codes
This includes predefined messages used in specific situations, ranging from simple messages like ‘I am disabled and need assistance’ to complex messages, which help convey urgent information quickly.
Special Signals
These indicate specific requirements or operations like a vessel engaged in towing or ship needing medical help.
Group Signals
This includes signals made by flying several flags together, creating a group that depicts a complete message. For eg. ‘I am in distress’ can be signalled by using a combination of flags, each one standing for a part of the message.
Challenges in Using INTERCO
Despite being universally used in the maritime industry, INTERCO also has a few limitations.
During rough seas and poor visibility, visual signalling can be difficult to interpret for the other party and even radio signals might be subject to interference.
All seafarers must be adequately trained in using the Code properly to ensure effective communication. Using the wrong code or signal in an emergency can be catastrophic.
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Source: Marine Insight
