My Dad and I can definately remember singing a hymm during our school days that was to the same tune as the German national anthem. Were they composed by the same person? Did the composer of one like the sound of the other? And what is the name of that hymm?
The national anthem is “Deutschlandlied”, formerly (before some of the lyrics were excised) called “Deutschland über Alles.” The music, but not the words, are by Haydn, in a song called “the Austrian Song”, “the Austrian Hymn”, or “the Austrian Imperial Anthem”. There is at least two religious hymns, and probably more, that have used the same music
Glorious Things of Thee are Spoken = Deutschland, Deutschland Ueber Alles = “Austrian Kaiserhymn” - String Quartet, Op.76, No 3, 2nd movement by Franz Josef Haydn (can’t find a listening link) = German National Anthem, adopted 1952
“Franz Haydn’s Austrian Hymn, taken from one of his string quartets, was first performed for the Emperor Francis II’s fifth birthday. Today, it is the most common melody to which we sing the popular hymn “Glorious Things of Thee Are Spoken.” It is the melody as well for the German national anthem Deutschland, Deutschland über Alles. I once was in a Holocaust service in a parish in which the priest chose the hymns (I was a choir member) had the insensitivity to choose that hymn, tainted as it is by Nazi associations. On the same day in 1938, German troops entered Austria.”
From The German National Anthem: its text and its history
“The President and the Chancellor thus took account of the practice of the last forty years, which has been that the third verse alone is sung, not just on State occasions but also at other events. Nonetheless their ruling does not forbid the printing and singing of the full version of the anthem on non-State occasions.”
As far as I can tell, the original German title was “Gott erhalte Franz den Kaiser.” (God Save Kaiser Franz).
Up until the 1930s, the tune was just a pretty tune, and a number of songs both secular and sacred were set to the same music. One that pops to mind immediately is the Alma Mater of my alma mater (University of Pittsburgh).
For obvious reasons, the song lost popularity during and after WWII, and some uses of it were scrapped. The hymnal used by the church of my youth had “Praise the Lord, ye heavens adore him” set to an entirely different tune (with the same meter) - probably the “Hyrfrydol” mentioned in one of the links above. It was quite a surprise for me to hear it set to the original Haydn melody the first time.
I know that the hymne was “Deutschland Deutschland über alles” during WW 2. 
But isn’t the original Alle Menschen wirden Brüder ?
*All peoples will be brothers [and sisters, I guess.:)] *
The “Alle Menchen wirden Brueder” tune is from Beethoven’s 9th Symphony, also called Hymn of Joy and translated into a least one popular English language church hymn. It was sung at our wedding back when in the days when the congregation was expected to provide the wedding music themselves. The opening line of the chorale is “Freude, Freude…schoenes Gotterfunken…” (Joy, Joy…beautiful devine spark…) or something vaguely like that. The chorale is based on a poem by (I think) Goethe. Please excuse my German; it has been a long time and I don’t seem to have an umlaut.
(Just as an aside) I remember an old film about British POW’s in a German camp singing “Glorious Things of Thee Are Spoken” to annoy the guards.
thank you.
But you * do * have an umlaut. just the " above a letter. 
[And your German is better than mine. And I’m a neighbour!]
Pretty close. The words were from the poem “An die Freude” by Schiller, the words of which may be found on this page. The opening line is “Freude, schoener Goetterfunken, Tochter aus Elysium”. The line you mention appears in the first stanza (but it’s Menschen).
And that hymn is Joyful, Joyful, We Adore Thee.
That song plays as part of the angelus (6PM bells) of the Chicago Temple,* and when I worked around the corner from the Temple I always wondered about that song because the only other place I heard it was as the background theme music for when the Germans were doing something in a WWI or II movie.
Now I know … the REST of the story.
*Chicago Temple is a Protestant church (I forget the denomination) in a 20-something story Gothic-style skyscraper, topped with a big church spire, across from the county courthouse and kittycorner from City Hall.