SOS is an internationally accepted Morse Code distress signal, which is used for requesting help in times of crisis.
Before the acceptance of SOS as an internationally accepted distress signal in 1908, there was another distress call being used, which was CQD. However, even before CQD was invented, there was no way for ships that were isolated from their harbor or other ships, to ask for help in times of crisis. For centuries it happened that a ship would sink somewhere in sea, and its fate would be a mystery to everyone else who wasn't on the ship. This is the reason why there was a need to invent a medium through which ships encountering problems at sea could contact a nearby station for help. This medium was finally provided by the invention of wireless telegraph and Morse Code.
The letters CQD became the first ever signal of distress call by the year 1904, when almost all transatlantic ships had wireless telegraph capability on board. CQD, as many people reckon, doesn’t stand for “Come Quick Danger”, but it means “All stations, distress”. The letters CQ when preceded by any message denoted All stations, so as to say: “All stations, be informed”, and the rest of the message would follow immediately.
However, it had been noticed around this time that there was no internationally agreed upon distress call in the world. Britain was using CQD as its official distress call, whereas Germany used SOE as their official call for help. Likewise, many other nations were probably using their very own official distress calls. Which is why, this matter was taken up to be debated at the Radiotelegraphic Conference in Berlin, in 1906. The participants agreed to the fact that multiple distress calls can only cause ambiguity, so there was a need for a distress call that would be universally accepted. As a result, SOS was chosen as the new international distress call, and became effective on July 1, 1908.
As it happened with CQD, the SOS distress call has also been understood to be an acronym/abbreviation/initialism for: “save our ship”, “save our souls”, or “send out succor”. However, the fact is that SOS isn’t an acronym at all. Actually, it doesn’t stand for any words starting from S, O and S. These letters were selected because they can be easily remembered in a Morse Code sequence. In Morse Code, the letter S is represented by 3 dits (dots) and the letter O by 3 dahs (dashes). So, the letters SOS put together in Morse Code would look like this: (· · · – – – · · ·)
It was found that this code could also be written in several other ways in Morse, but they were all 8-element signals. SOS was one among the many ways to convey this code, but it did so as a 9-element signal (3 dits, 3 dahs, and 3 dits). Since no other signal used more than 8 elements, SOS was readily recognizable and chosen as the new universal distress call. From the date of its acceptance, many ships began to use this signal in times of danger. Most notably, RMS Titanic did so in 1912. The Titanic's radio operator had first sent the CQD distress call. However, a few moments later, the operator also sent SOS, when another crew member opined that SOS was the new universally accepted signal. Unfortunately, the ship could not be rescued and sank eventually. This occurence is regarded as one of the most tragic events in world maritime history.
The importance of SOS is relevant in today's world, in this current age of technological advancement as well. Many mobile phone and mobile application developers have come up with apps that send out messages for help to a person's relatives and also the nearby authorities. These applications first ask the user to input a set of numbers that he/she would call when in danger. These numbers could be of one's parents, teachers, friends, relatives, etc. Besides these numbers, the application also stores the emergency service number applicable to the location that the person is residing in. For instance, a person in America using an app like this, will have the emergency number 911 stored by default through the application, and a person living in the United Kingdom would have 999 stored as the emergency service number. Reasons like these make such applications come in handy. Of late, applications like these are in great demand, as they have helped many people, and highlighted the importance of distress signals like SOS.