What is flag semaphore?

Flag semaphore is a visual signalling system in which a person holds a flag in each hand and positions the arms at set angles to spell out letters and numbers. It was widely used at sea for ship-to-ship communication.

How are the arm positions described?

Each arm points to one of eight positions around the body, like points on a clock or compass. A character is defined by the combination of where the two flags point, shown in the diagram as two lines from a central point.

How are numbers signalled?

There is no separate set of number positions. The signaller sends the Numerals sign, after which the positions for letters A through K stand for digits 1 through 0, until the Letters sign switches back.

Is the J position special?

Yes. The letter J shares its position with the Letters sign, which is used to switch back from numerals to letters. Context tells the reader whether a J or a mode switch is intended.

Is semaphore still used today?

It is largely historical, replaced by radio, but it is still taught for emergencies and ceremonial use, and remains part of scouting and naval training. Knowing the chart is useful for puzzles and signalling drills.

What is the Semaphore Flag Alphabet Reference?

Visual reference for maritime flag semaphore: see the two-flag arm positions for all 26 letters and the numeral system, with searchable diagrams showing each character at a glance. It runs free in your browser on Gera Tools, with nothing uploaded.

Semaphore Flag Alphabet Reference

Name: Semaphore Flag Alphabet Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Semaphore flag alphabet reference

Flag semaphore lets two people communicate across a distance by holding a flag in each hand and positioning the arms at fixed angles. Each letter is a unique pair of arm positions. This reference shows a clear diagram for every character so you can encode or decode a message at a glance.

How the positions work

Imagine eight positions evenly spaced around the signaller’s body, like the points of a compass: down, lower-left, left, upper-left, up, upper-right, right, lower-right. Each arm independently points to one of these eight positions, giving 64 possible combinations — more than enough to cover the 26 letters plus mode signs.

The alphabet is not arbitrary: letters progress in an orderly way. A through G keep one arm pointing straight down while the other sweeps around from lower-right through to left. H onward shifts the base arm up to lower-left, and the second arm continues sweeping. This systematic layout is what lets operators memorise the alphabet: once you know the first group, subsequent groups follow the same sweep pattern with a different base.

Numbers reuse letter positions. The signaller first sends the Numerals sign; after that, the positions normally meaning A through K stand for the digits 1 through 0. The Letters sign (which shares J’s position) switches back to ordinary letters.

History and context

Flag semaphore was developed for naval communications in the early 19th century and became a standard signalling method for maritime and military use long before radio. The Royal Navy formalised a system around 1816. At range — anything from a few hundred metres to a mile or more in clear conditions with binoculars — it allowed real-time communication between ships and shore stations without any electrical infrastructure.

The system is still used for ceremonial purposes, in scouting programmes, and as part of naval and maritime training worldwide. It also appears frequently in escape rooms, puzzle hunts, and ARGs, where puzzle designers appreciate that it requires a reference chart to decode without training.

Speed and practical limits

An experienced operator can signal at roughly 25–30 words per minute. That is slower than Morse code tapped by key but faster than most people can achieve with Morse flags. The main practical limit is line of sight and lighting — semaphore fails in darkness, fog, or at long ranges without optical aids, whereas radio signals these conditions. This is why radio displaced semaphore for operational naval communication.

Tips and notes

The diagrams are drawn as seen facing the signaller, so their right arm is on your left in the diagram. Mirror the image if you are the one sending.
Because numerals borrow letter positions, always send the mode signs at transitions — a message read in the wrong mode turns every digit into the wrong letter.
For puzzle use, the Numerals and Letters mode signs are the most commonly forgotten element — include them explicitly in encoded messages to avoid ambiguity.
Semaphore is slower than Morse but needs no equipment at all, which is why it endured for line-of-sight naval signalling for over a century before radio.