When did SOS (· · · — — — · · ·) become the international distress signal ?

right after the sinking of the Titanic, the distress signal was originally CQD, not sure what the acronym stands for but the story goes that the Titanic sent out the distress signal and on the ships that received the code it was not understood, one German ship was very close to the Titanic, much closer than the Carpathia but pre war tensions between the Brits and the Germans prevented any miscues from being cleared up. Neither camp had any patience for the other to translate so the signal was changed to SOS, or Save Our Ship, easily understandable and a better coded relay to anyone whom was within range to assist. So the year was April of 1912.