DatumFlag — International Code of Signals
Master maritime flag signals with DatumFlag, the third app in the Datum trilogy. Built for seafarers, cadets, amateur radio operators, and anyone fascinated by the elegant visual language of the sea.
COMPLETE ICS REFERENCE
Browse all 40 international signal flags — 26 letter flags, 10 numeral pennants, the answering pennant, and 3 substitutes. Each flag entry includes its letter designation, phonetic name, NATO phonetic alphabet, Morse code, single-flag meaning, and design description. Flags with semaphore positions show an animated stick figure demonstrating the correct arm positions from the viewer's perspective.
TWO-FLAG SIGNAL CODES
Explore the full catalogue of two-flag signal codes used in ship-to-ship and ship-to-shore communication. Filter by category — distress, navigation, manoeuvres, medical, meteorological, and more. Each signal shows its component flags with meanings and full signal interpretation.
SEMAPHORE TRANSMITTER
Type a message and watch it transmitted letter by letter in flag semaphore. An animated signaller raises and lowers flags through the correct positions for each character, with transmitted letters appearing as their corresponding ICS flags beneath. Adjust signalling speed from Cadet to Yeoman.
EIGHT QUIZ MODES
Test your knowledge across eight distinct quiz modes:
Flag → Meaning: identify what a flag signals
Meaning → Flag: find the flag for a given meaning
Flag → Letter: name the letter a flag represents
Letter → Flag: pick the correct flag for a letter
Phonetic → Flag: match NATO phonetic words to flags
Morse → Letter: decode Morse code to letters
Signal → Meaning: interpret two-flag signal codes
Semaphore → Letter: read semaphore arm positions
Choose from 10, 20, or 40 questions per session, or select Endless mode. Three difficulty levels control the number of answer options presented.
RETRO CRT AESTHETIC
DatumFlag renders everything through a phosphor-screen aesthetic inspired by vintage computer terminals. Choose between classic green and warm amber colour themes. The interface evokes the glow of a bridge console or signals office CRT — because maritime communication deserves more atmosphere than a flat white screen.
PART OF THE DATUM SERIES
DatumFlag joins DatumLight (lighthouses and navigation aids) and DatumMark (sea marks and buoyage systems) in the Datum series — a collection of focused reference tools built for clarity and offline use.
No account required. No network connection needed. No subscriptions. Just signals.
