Title: God Save the Queen
Content:  "God Save the Queen" (God Red die Koningin, God Red die Koning when a King) was a co-national anthem of South Africa from 1938 until 1957, when it was formally replaced by "Die Stem van Suid-Afrika" as the sole national anthem. The latter served as a sort of de facto co-national anthem alongside the former until 1938.
Title: God Save the Queen
Content:  "God Save the Queen", alternatively "God Save the King" (dependent on the gender of the reigning monarch), is the national or royal anthem in most Commonwealth realms, their territories, and the British Crown dependencies. The author of the tune is unknown, and it may originate in plainchant; but an attribution to the composer John Bull is sometimes made. "God Save the Queen" is the de facto national anthem of the United Kingdom, and one of two national anthems used by New Zealand since 1977, as well as for several of the UK's territories that have their own additional local anthem. It is also the royal anthem – played specifically in 
Title: God Save the Queen
Content:  "God Save the King/Queen" was exported around the world via the expansion of the British Empire, serving as each country's national anthem. Throughout the Empire's evolution into the Commonwealth of Nations, the song declined in use in most states which became independent. In New Zealand, it remains one of the official national anthems.
Title: God Save the Queen
Content: Not on this land alone ; But be God's mercies known ; From shore to shore. ; Lord, make the nations see ; That we in liberty ; Should form one family ; The wide world o'er. "God Save the Queen" was the sole official national anthem until 1977 when "God Defend New Zealand" was added as a second. "God Save the Queen" is now most often only played when the sovereign, governor-general or other member of the Royal Family is present, or on some occasions such as Anzac Day. The Māori-language version was written by Edward Marsh Williams under the title, "E te atua tohungia te kuini". There is a special New Zealand verse in English which was once commonly sung to replace the second and third verses:
Title: God Save the Queen
Content:   Like many aspects of British constitutional life, "God Save the Queen" derives its official status from custom and use, not from Royal Proclamation or Act of Parliament. The variation in the UK of the lyrics to "God Save the Queen" is the oldest amongst those currently used, and forms the basis on which all other versions used throughout the Commonwealth are formed; though, again, the words have varied over time. England has no official national anthem of its own; "God Save the Queen" is treated as the English national anthem when England is represented at sporting events (though there are some exceptions to this rule, such as cricket where "Jerusalem" is used). There is a movement to establish an English national anthem, with Blake and Parry's "Jerusalem" and Elgar's "Land 
Title: God Save the Queen
Content:  melody was also used for the national anthem 'Heil dir im Siegerkranz' of the German Empire from 1871 to 1918 and as "The Prayer of Russians", the imperial anthem of Russia from 1816 to 1833. In Switzerland, it is known as "Rufst du, mein Vaterland". Beyond its first verse, which is consistent, "God Save the Queen/King" has many historic and extant versions. Since its first publication, different verses have been added and taken away and, even today, different publications include various selections of verses in various orders. In general, only one verse is sung. Sometimes two verses are sung, and on rare occasions, three. The sovereign and her or his 
Title: God Save the Queen
Content:  The standard version of the melody and its key of G major are still those of the originally published version, although the start of the anthem is often signalled by an introductory timpani roll of two bars length. The bass line of the standard version differs little from the second voice part shown in the original, and there is a standard version in four-part harmony for choirs. The first three lines (six bars of music) are soft, ending with a short crescendo into "Send her victorious", and then is another crescendo at "over us:" into the final words "God save the Queen". In the early part of the 20th century there existed a Military Band version in the higher key of B, because it was easier for brass instruments to play in that key, though it had the disadvantage of being more difficult to sing: however now most Bands play it in the correct key of concert F. Since 1953, the anthem is sometimes preceded by a fanfare composed by Gordon Jacob for the coronation of Queen Elizabeth II.
Title: God Save the Queen
Content:  In Australia, the song has standing through a Royal Proclamation issued by Governor-General Sir Ninian Stephen on 19 April 1984. It declared "God Save the Queen" to be the Royal Anthem and that it is to be played when the Australian monarch or a member of the Royal Family is present, though not exclusively in such circumstances. The same proclamation made "Advance Australia Fair" the national anthem and the basis for the "Vice-Regal Salute" (the first four and last two bars of the anthem). Prior to 1984, "God Save the Queen" was the national anthem of Australia. In 1975 former Prime Minister Gough Whitlam, dismissed by Governor-General Sir John Kerr, alluded to the anthem in his comment "Well may we say 'God save the Queen', because nothing will save the Governor-General!".
Title: God Save the Queen
Content:  It became the anthem of the Austrian Empire after the end of the Holy Roman Empire with revised lyrics, its tune ultimately being used for the German national anthem. The tune of "God Save the King" was adopted for the Prussian royal anthem "Heil Dir im Siegerkranz". Franz Liszt wrote a piano paraphrase on the anthem (S.259 in the official catalogue, c. 1841). Johann Strauss I quoted "God Save the Queen" in full at the end of his waltz Huldigung der Königin Victoria von Grossbritannien (Homage to Queen Victoria of Great Britain) Op. 103, where he also quoted Rule, Britannia! in full at the 
Title: Anthems and nationalistic songs of Canada
Content:  "God Save the Queen" is the royal anthem of Canada. There are various claims of authorship and several previous songs of similar style, but the first published version of what is almost the present tune appeared in 1744 in Thesaurus Musicus. The song has been used in Canada since the era when it was a collection of British colonies and "God Save the King" (or "God Save the Queen" during the reign of Queen Victoria) was played in honour of the British monarch. It has remained in use through Canada's progression to independence, becoming eventually one of the country's two de facto national anthems. After "O Canada" was in 1980 proclaimed the national anthem, "God Save The Queen" has been performed as the royal anthem, in the presence of the Canadian monarch, other members of the Royal Family, and as part of the salute accorded to the Governor General of Canada and provincial lieutenant governors, as well as on other occasions.

Question: when did god save the queen became the national anthem?
Answer: in the 1780s and 1790s.
After the Battle of Culloden.