I first heard the hymn “I Vow to Thee, My Country” while watching the first season of The Crown . I assume the hymn is familiar in the UK, but it is not in America as far as I know.
When I say I first heard the hymn, I mean that I first heard it as a hymn with words. I thought the tune sounded familiar, and that it reminded me of The Planets by Holst.
I’ve started watching the latest season of The Crown and once again I heard the hymn , so this time I looked into it more. The tune does indeed come from The Planets, specifically from the middle of the Jupiter movement.
With a little searching I found the sheet music to the hymn.
This brought up more things I’ve long meant to look into. As a child I remember cryptic notations around hymns, such as “Thaxted 13.13.13 D” above, and never knew what they meant.
Tunes have names independent of the hymns they appear in, but these tune names were, and still are, completely unfamiliar to me. For example, the hymn “Amazing Grace” has the tune “McIntosh,” though I don’t imagine many people know that.
In the example here, “Thaxted” is the name of the melody from Jupiter when it is used as a hymn. The name comes from the English town of Thaxted where Holst lived. Perhaps there are other hymns that use the same tune.
Now what about the mysterious numbers 13.13.13? They mean that the hymn is built out of groups of three lines, each with 13 syllables. The hymn Once in Royal David’s City is marked 87 87 77, meaning the hymn has three phrases, the first two alternating lines of 8 and 7 syllables, and the last having two lines of 7 syllables each.
From what I’ve read, the “D” in “13.13.13 D” stands for double meter, which I would take to mean 2/4, but the tune is clearly in 3/4, so I’m not sure what the D means.
Update: The D means the entire pattern is doubled, not that the meter is double time. Thaxted has six lines, in two groups of three. Thanks to Michael Lugo for letting me know via Twitter.
 S1E1 10:00
 S4E3 40:30