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How to speak in flags

Do you know the real meaning of Blue Peter? Or how many flags show the international sign for distress at sea? What would tell someone they’re about to run into danger – or you’d like to borrow their newspaper? Let’s find out. 

Boulmer pulling and sailing boat Arthur R. Dawes is in the distance at sea. A man is in the shallow water, up to his knees and giving the sailing boat the letter 'J' signal by flags.

Photo: RNLI

Like the RNLI, using flags to send messages at sea has a long and rich history. Just hours before the Battle of Trafalgar in 1805, Lord Nelson used a flag code from the Telegraphic Signal of Marine Vocabulary to send the infamous message: ‘England expects that every man will do his duty’. 

An evolution of language

Developing on the Telegraphic Signal of Marine Vocabulary, novelist and naval man Captain Frederick Marryat created A Code of Signals for the Merchant Service at the start of the 19th century – and it quickly became the most widely used flag code among seafarers, especially as it translated into other languages.

Marryat believed there was an urgent need for more effective communication at sea: ‘The master of a merchant vessel who sees another steering into danger has, at present, no means to warn her of it – but must endure the agonising sensation of following her with his eye, till she is dashed to pieces on the rocks. Had she been able to communicate … the crew at least, if not the vessel, might have been saved.’

Many messages in Marryat’s flag code helped people explain navigational details to one another, such as longitude, or a warning that an entrance was narrow. Others asked messages of health, such as: ‘Has the plague ceased?’ and ‘Was the port you left healthy?’ 

Some of Marryat’s messages helped seafarers send warnings of pirates, while others dealt with more important matters such as: ‘Can you lend us your newspapers?’

Marryat’s code eventually evolved in 1855 into the International Code of Signals (ICS) – helping provide mariners with an internationally accepted, common system for communicating at sea. Each individual signal has a complete meaning to ensure specific situations can be clearly and quickly communicated, even when language barriers arise. 

The ICS is still used today – and the distress signals are taught by RNLI Water Safety teams as part of their maritime search and rescue education. 

The International Code of Signals 

As well as numbers from 1 to 10, the ICS contains a standardised alphabet from A to Z. Each flag represents a letter with its own individual meaning attached. And each flag can be raised alongside another to expand on the situation or message that a vessel is trying to communicate. 

The International Code of Signals, alphabetised from A to Z

Photo: RNLI

The International Code of Signals - each flag represents a letter with its own individual meaning attached

Single-letter signals (where one flag is raised), are the most urgent or important. Raising your ‘U’ flag will quickly let others know: ‘You are running into danger.’ And raising the ‘K’ flag will give the heads up to a nearby crew that you want to communicate with them.   

Did you know the ‘P’ flag stands for Blue Peter – and was the inspiration for the BBC children’s programme with the same name? It translates to: ‘We’re in harbour, getting ready to set sail’. 

Two-letter signals (where two flags are raised), are used to supplement or explain a message further. The most urgent code for help is the ‘N’ flag arranged above the ‘C’ flag – this is the International Code Signal of distress. 

The ‘N’ flag is positioned above the ‘C’ flag which is the International Code Signal of distress and signifies the most urgent call for help at sea.

Photo: RNLI

The ‘N’ flag positioned above the ‘C’ flag, which is the International Code Signal of distress and signifies the most urgent call for help at sea

Translated, these two flags together literally read as: ‘No Yes’. We can interpret that to mean: ‘No, it’s not good’. If you see this signal of distress out on the water, dial 999 or 112 and ask for the coastguard.

Another example of a two-letter signal is to raise the ‘M’ flag with the ‘Y’ flag – which translates as ‘My vessel has stopped’ and ‘I am dragging my anchor.’ You’d be letting people nearby know that this area is a dangerous or shallow place to stop. 

The ‘M’ flag is positioned next to the ‘Y’ flag, which will let a nearby vessel know that the area is a dangerous or shallow place to stop.

Photo: RNLI

The ‘M’ flag positioned next to the ‘Y’ flag lets nearby vessels know that the area is a dangerous or shallow place to stop

For every one 

A huge benefit of the ICS is that the manual for understanding the flags comes in nine different languages – English, French, Italian, German, Japanese, Spanish, Norwegian, Russian and Greek. So, even if the message sender and receiver speak different languages, they are both connected to the same code that they mutually understand. 

The code also offers a more inclusive way to communicate at sea. The flags don’t require a specific skill to operate them and they don’t rely on noise or audio. Plus, they don’t need a power source to run.

Quiz yourself: What are these flags saying?

Let’s test your flag-reading skills so far (you’ll find the answer below, so no sneaky scrolling!) 

Using the ICS, what is this message saying?

The ‘G’ flag is positioned next to the ‘M’ flag, which will let a nearby vessel know that you are stuck and can’t help yourself.

Photo: RNLI

The 'G' flag is positioned next to the 'M' flag – what does it mean?

a) Keep clear and stay at slow speed.
b) I can’t save my vessel.
c) Stop your vessel immediately!
d) Will you give me my position? 

The big reveal (no cheating, now!)

If you answered B, you’re correct. Flags ‘G’ and ‘M’ literally translate to ‘I need a pilot’ and ‘my vessel is stopped – I’m making no way through the water.’ So you’d be letting someone nearby know that you’re stuck, and you can’t help yourself. 

From here, the message receiver can come to your aid if it’s safe to do so, or they can alert the coastguard and RNLI volunteers will drop everything to help you.  

Brush up on your flag-speaking skills and help teach your family something new with our fantastic range of ICS products from RNLI Shop. From signal-savvy tea towels to message-making mugs, we’ve got you covered – and every purchase you make goes towards saving lives at sea. That makes you a lifesaver too.