Question: Which British patriotic hymn created in 1921 was a unison song with an orchestra?

Context paragraphs:
Hymno Patriótico: The Hymno Patriótico (English: "Patriotic Hymn" ), was considered Portugal’s first national anthem.  Marcos Portugal, who had remained living in Portugal, had, in 1808, initially named the piece as ‘the Prince’s Hymn’ ("D. João VI Hymn").  With this dedication, it was offered to the Prince Regent D. John and first performed for him in Brazil in 1809.  The anthem was inspired by the cantata “La Speranza o sia l’Augurio Felice”.  The lyrics changed several times, altered by contemporary events, until settling into a more or less permanent form in 1821.

Thaxted (tune): "Thaxted" is a hymn tune by the English composer Gustav Holst, based on the stately theme from the middle section of the "Jupiter" movement of his orchestral suite "The Planets" and named after Thaxted, the English village where he resided much of his life.  He adapted the theme in 1921 to fit the patriotic poem "I Vow to Thee, My Country" by Cecil Spring Rice but that was as a unison song with orchestra.  It did not appear as a hymn-tune called "Thaxted" until his friend Ralph Vaughan Williams included it in "Songs of Praise" in 1926.  This setting was sung at the Funeral of Diana, Princess of Wales, in 1997.

Song of Liberty: "Song of Liberty" is a British patriotic song which became popular during the Second World War.

National anthem of the Korean Empire: The "Patriotic Hymn of the Korean Empire" (Hangul: 대한제국 애국가 ; Hanja: 大韓帝國 愛國歌 ; literally "Korean Empire Aegukga") was the national anthem of the Korean Empire, used in the early 20th century.  It was the first national anthem of a unified Korean state.

Cecil Spring Rice: Sir Cecil Arthur Spring Rice {'1': ", '2': ", '3': ", '4': "} (27 February 1859 – 14 February 1918) was a British diplomat who served as British Ambassador to the United States from 1912 to 1918.  In this role he was responsible for leading British efforts to end American neutrality during the First World War.  He is best known as the writer of the lyrics of the patriotic hymn, "I Vow to Thee, My Country".  He was also a close friend of US President Theodore Roosevelt, and served as best man at his second wedding.

God Bless America Again (song): "God Bless America Again" is a country music song written by Bobby Bare and Boyce Hawkins.  A patriotic hymn pleading for God's forgiveness of the United States and his guidance over the country, the song was first recorded and made famous by Bare.  Released as a single in 1969, Bare's version reached No. 16 on the "Billboard" Hot Country Singles chart.

Belgium Put the Kibosh on the Kaiser: Belgium Put the Kibosh on the Kaiser was a popular British patriotic song of the First World War.  It was first recorded on 6 October 1914 by Mark Sheridan.  The song refers to the 1914 campaign in Belgium when the small British Expeditionary Force, along with an unexpectedly fierce Belgian defence, managed to delay the much larger German army, slowing them and wrecking the Schlieffen Plan which depended on total victory against the French to the west in a matter of weeks.  By attacking Belgium, they had violated that nation's neutrality and brought the British Empire into the war because of a pledge to uphold Belgian independence.  The song has the metre of Tramp!  Tramp!  Tramp! .

Max Schneckenburger: Max Schneckenburger (18 July 1819 – 3 May 1849) was a German poet.  The patriotic hymn "Die Wacht am Rhein" uses the text of a poem Schneckenburger wrote in 1840.

I Vow to Thee, My Country: "I Vow to Thee, My Country" is a British patriotic hymn, created in 1921, when a poem by Sir Cecil Spring Rice was set to music by Gustav Holst.

Rule, Britannia!: "Rule, Britannia!"  is a British patriotic song, originating from the poem "Rule, Britannia" by James Thomson and set to music by Thomas Arne in 1740.  It is strongly associated with the Royal Navy, but also used by the British Army.

Supporting paragraphs: Thaxted (tune) I Vow to Thee, My Country
Answer: I Vow to Thee, My Country