SOS in Morse Code: Meaning, History & How to Signal It

SOS is the international Morse code distress signal, transmitted as the contiguous sequence ... --- ... (three dots, three dashes, three dots) sent as a single unbroken prosign with no inter-letter pauses. Unlike most Morse code, where letters are separated by a brief silence, SOS is sent as one continuous burst so that any operator hearing it through heavy interference or static instantly recognizes the pattern.

The signal was adopted as the international maritime distress call at the second International Radiotelegraphic Convention in Berlin on November 3, 1906, replacing the older CQD signal used by the Marconi company. It went into effect on July 1, 1908. The choice was pragmatic: the symmetrical pattern of three-three-three is unmistakable, easy to send even by an exhausted or injured operator, and easy to recognize under poor reception conditions.

Despite the popular myth, SOS was never intended as an abbreviation for “Save Our Souls” or “Save Our Ship.” Those are backronyms invented after the fact to help people remember the pattern. The letters were chosen purely for their Morse simplicity. The backronyms persist in popular culture and serve as a useful mnemonic, but they are not the origin of the signal.

You can transmit SOS with virtually any signaling device capable of producing two distinct durations (short and long). The most common methods are:

• Flashlight or mirror: Three short flashes, three long flashes (about three times longer), three short flashes. Pause, then repeat.
• Whistle or horn: Three short blasts, three long blasts, three short blasts. Useful in fog or mountainous terrain.
• Radio: Key the carrier on and off in the dit-dah-dit pattern. Amateur radio operators still practice this on HF bands.
• Tapping: Tap on a wall, pipe, or hull: three light taps, three heavy taps, three light taps. Used by trapped miners and submariners.
• Flag or arm signals: The ground-to-air distress signal is a triangle (V) of three, but the Morse pattern can be flagged with two cloth squares moved in short-long-short bursts.

Whatever the medium, the key is repetition. Send the pattern continuously, with a brief pause between each SOS group, until you receive a response or are rescued. A single SOS may be missed; a repeating SOS will not be.

The most famous SOS in history was sent by the RMS Titanic on the night of April 14 to 15, 1912. The ship's senior wireless operator, Jack Phillips, initially sent the older CQD signal, then switched to SOS, reportedly quipping that it was the new call and it might be his last chance to use it. The Titanic's distress calls were received by the RMS Carpathia, which raced to the scene and rescued 705 survivors from the lifeboats.

Other notable early SOS transmissions include the RMS Republic (January 1909, one of the first major rescues enabled by an SOS distress call) and the SS Slavonia (June 1909). The RMS Lusitania used SOS in 1915 when torpedoed during World War I. The signal saved thousands of lives during the era when wireless telegraphy was the primary means of maritime communication.