SOS
Before radio communication was developed in the early 1890s, seagoing ships had already adopted many different visual and audio distress signals. They used such things as semaphore flags, signal flares, bells, and foghorns. In the beginning, radio was called wireless telegraphy. It used Morse code, the dit-and-dah system originally developed for landline telegraphy.When radio communication was made available to ships, there was a need for standardized communication. Cooperation was somewhat limited by national differences and rivalries between different radio companies.