The International Code of Signals: purpose and layout
1The lesson in plain words
The International Code of Signals lets ships talk about safety without a shared language. Each signal has a complete meaning, sent by flag, light, sound or voice.
Purpose and editions
The International Code of Signals (ICS) gives ways to communicate about the safety of navigation and persons, especially when language is a problem. It was adopted in 1965 and came into force on 1 April 1969. IMO publishes it; the current text is the 2005 edition, later reprinted with only editorial changes. The US edition, NGA Pub. 102, contains the same signals and is free online.
Three kinds of signal
Single-letter signals carry very urgent, important or common meanings. Two-letter signals form the General Signal Code, arranged by subject: distress and emergency first, then casualties, navigation, manoeuvres, weather, communications and health. Three-letter signals beginning with M form the Medical Signal Code. The book also gives the signalling instructions, distress and life-saving signals, and radiotelephone procedures.
Complete meanings and complements
Each signal has a complete meaning, so you do not build sentences word by word. A numeral complement after a group varies or extends it. ‘IN’ means ‘I require a diver’; ‘IN 1’ means ‘I require a diver to clear propeller’. Three tables of complements give common variations: Table 1 lists ways to communicate, Table 2 kinds of assistance, Table 3 directions.
Methods
You may send ICS signals by flags, flashing light, sound, voice over a loud hailer, radiotelegraphy, radiotelephony, or Morse by hand flags or arms. By radio, say ‘INTERCO’ before Code groups and spell them with the phonetic alphabet. Whenever possible, use plain language; the Code is for when a language difficulty exists.
The flag set
A full set has 40 flags: 26 alphabetical flags, 10 numeral pennants, 3 substitutes and the answering pennant. Learn to recognise them on the Signal flags page and its game; this unit is about using them.
2Key data
- In force
- 1 April 1969 (adopted 1965); current IMO text: 2005 edition
- US edition
- NGA Pub. 102, same signals, free online
- Signal types
- 1 letter: urgent/common; 2: general; 3 starting with M: medical
- Flag set
- 26 letters, 10 numeral pennants, 3 substitutes, 1 answering pennant
- By radio
- Say ‘INTERCO’, then spell groups phonetically
3Key points
- 1
The ICS is for safety messages when ships do not share a language; each signal has a complete meaning.
- 2
Single letters are urgent or common; two-letter groups are general; M-groups are medical.
- 3
A numeral complement varies or extends a group’s meaning.
- 4
By voice or radio, ‘INTERCO’ announces that Code groups follow.
4Frequent mistakes
Wrong: The Code is only for signal flags.
Right: The same signals can be sent by flags, light, sound, loud hailer, radio, or hand flags and arms.
Wrong: Build a message letter by letter from single-letter meanings.
Right: Look up the group that has the complete meaning you need, with a complement if necessary.
Wrong: The Code must replace plain language in every exchange.
Right: Use clear plain language when suitable. Whenever you send Code groups by voice, announce them with INTERCO.
5Practice case & exam keys
At anchor off a small port you need to tell a nearby fishing vessel, whose crew speaks no English, that you require a diver to clear your propeller. Your VHF works. How can the Code help?
Show the answer
Call the vessel on VHF and say ‘INTERCO’, then spell the group ‘India November One’ with the phonetic alphabet. IN 1 means ‘I require a diver to clear propeller’; the crew can look it up in their own language edition. You could also hoist IN 1 with flags if they keep a visual watch.
Exam keys
- Purpose: safety of navigation and persons, especially with language difficulties.
- Single-letter, two-letter general and three-letter medical (M) signals.
- Complements vary or extend a group; INTERCO announces Code groups by voice.
- A flag set: 26 letters, 10 numeral pennants, 3 substitutes, answering pennant.
Finish this unit
When you've read it, answer three questions. Get all three right to finish the unit; opening the page alone doesn't count.
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