My music for Remembrance Day was not written specifically for the purpose of commemorating WW1, however it was written few years after the end of the war and was very much Vaughan Williams’ reaction to the war. Wikipedia suggests that it “has gained the reputation of being a subtly beautiful elegy for the dead of World War I and a meditation on the sounds of peace”.
I played this with Gli Amici soon after I came to Bournemouth. It is, perhaps, not as well known as some of his other music, but it certainly evokes the ‘pastoral’ as its title suggests. I particularly like the trumpet and horn solos.