The Nautical Alphabet and Signal Flags

The NATO Phonetic Alphabet

The NATO phonetic alphabet — also called the International Radiotelephony Spelling Alphabet — was designed to eliminate ambiguity in voice communication over noisy radio channels. Letters that sound similar (B, D, E, P, T, V) are replaced with distinctive words that cannot be confused even in poor conditions.

The 26-letter alphabet:

Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Note the spellings: Juliett has two t's. Foxtrot is one word. X-ray is hyphenated. Zulu is also used as the phonetic equivalent of UTC (Coordinated Universal Time) — you will hear 'zero-eight-hundred Zulu' to mean 0800 UTC.

Numbers are also standardized: zero, one, two, three, four, fife (not five), six, seven, eight, niner (not nine). The substitutions 'fife' and 'niner' prevent confusion with 'five' (which sounds like 'fire' in many accents) and 'nine' (which sounds like the German word 'nein').

Where you will use this: spelling a vessel name, waypoint name, or unusual location over VHF. When calling the Coast Guard, marina, or another vessel and your boat name is unusual or ambiguous. In an emergency, the ability to spell your vessel name clearly over a radio without repeating yourself can save critical time.

Single-Letter Signal Flag Meanings

The International Code of Signals (ICS) assigns a unique flag to each letter of the alphabet. When flown singly — one flag alone — many of these flags carry an urgent or standardized meaning that all mariners are expected to know. These single-letter signals predate radio and were the primary means of ship-to-ship communication for centuries.

Alpha (A) — Blue and white divided flag: 'I have a diver down; keep well clear and proceed at slow speed.' This is the flag you must fly whenever a diver is in the water. Flying Alpha is legally required in most jurisdictions and a matter of life safety — a passing vessel's wake can disorient or injure a diver below.

Bravo (B) — Solid red flag: 'I am taking on, carrying, or discharging dangerous cargo (fuel).' Flown at fuel docks and on vessels taking on fuel. Prohibits open flames, smoking, and unshielded electrical equipment in the vicinity.

Charlie (C) — Blue, white, red, white, blue horizontal stripes: 'Yes' or 'affirmative.' A general acknowledgment signal.

Delta (D) — Yellow, blue, yellow vertical stripes: 'Keep clear — I am maneuvering with difficulty.'

Echo (E) — Blue and red divided flag: 'I am altering course to starboard.'

Foxtrot (F) — Red and white diamond pattern: 'I am disabled; communicate with me.' This flag indicates a vessel with a mechanical problem that needs assistance but is not in immediate distress.

Golf (G) — Yellow and blue vertical stripes: 'I require a pilot.' Also used by vessels entering unfamiliar ports.

Hotel (H) — White and red vertical halves: 'I have a pilot on board.'

November (N) — Blue and white checkerboard: 'No' or 'negative.' Paired with Charlie/November to form the distress signal NC.

Oscar (O) — Red and yellow diagonal halves: 'Man overboard.' One of the most important flags afloat. If you see Oscar flying on any vessel, that vessel has someone in the water.

Papa (P) — Blue square on white background: In port: 'All persons should report on board; the vessel is about to proceed to sea.' At sea: 'Your lights are burning badly' (or 'Your nets, lines, or trawl are foul.').

Quebec (Q) — Solid yellow flag: 'My vessel is healthy and I request free pratique' — the clearance to proceed into port after arriving internationally. The Q flag indicates you have not yet cleared customs.

Sierra (S) — White square on blue background: 'My engines are going full speed astern.'

Victor (V) — Red X on white background: 'I require assistance.'

Whiskey (W) — Red square on blue and white cross: 'I require medical assistance.'

X-ray (X) — Blue X on white background: 'Stop carrying out your intentions and watch for my signals.'

Yankee (Y) — Red and yellow diagonal stripes: 'I am dragging my anchor.'

VHF Radio Protocol

VHF radio is the primary communication tool for short-range maritime communication and distress calling. Understanding channel assignments and radio procedure is as fundamental as knowing your navigation lights.

Channel 16 — the universal distress and calling channel: Channel 16 is the international distress, safety, and calling channel. All vessels equipped with VHF radio must maintain a continuous watch on Ch 16 while underway. You use Ch 16 to hail another vessel or marina, then switch to a working channel once contact is established. You never conduct extended conversations on Ch 16.

Channel 9 — recreational boater hailing channel (US): The FCC has designated Ch 9 as an alternative hailing channel for recreational boats in the United States, which reduces routine traffic on Ch 16.

Channel 22A — Coast Guard liaison: The USCG communicates with recreational vessels on Ch 22A after initial contact on Ch 16. All USCG Urgent Marine Information Broadcasts (UMIB) and Notice to Mariners are broadcast on Ch 22A.

Channel 70 — Digital Selective Calling (DSC): Ch 70 is reserved exclusively for DSC digital calling. DSC is the modern automated distress system — pressing the red distress button on a DSC-equipped radio transmits your vessel's MMSI (Maritime Mobile Service Identity), GPS position, and vessel identity automatically. This is the fastest way to alert the Coast Guard in an emergency. Never transmit voice on Ch 70.

Standard radio call procedure:

1. '[Other vessel name], [other vessel name], [other vessel name], this is [your vessel name], [your vessel name], over.'

2. Once contact is made: '[Other vessel], this is [your vessel] — switch to channel [working channel], over.'

3. On the working channel: conduct your conversation, keep it brief and professional.

4. End the call with 'Out.' (conversation complete and radio closed) or 'Over.' (awaiting reply).

MMSI registration: if your VHF has DSC capability, you must register your MMSI number with the FCC or BoatUS/Sea Tow before use. An unregistered DSC distress call will generate a false alarm response that may direct rescuers to the wrong vessel.