There were veterans that I met in the 1980s who still believed in the legend of the Angels of Mons, and who would get quite emotional, despite the fact that the whole story was simply that, a story, and not even a story about angels for that matter.
I was looking through some old issues of The Great War, I Was There earlier today. I bought my set from a little second-hand bookshop just around the corner from the Imperial War Museum in 1981 and I still think it's a very useful resource. I particularly like the comments in the Old Comrades Corner section which I indexed many years ago and may publish one day.
Issue two of TGWIWT contains an article by the author behind the story and I reproduce that here. But first, here are the key passages from Arthur Machen's original article which detail the moment that the bowmen appeared to the BEF as they poured bullets into the massed ranks of advancing German infantrymen. The complete collection by Machen can be downloaded free of charge from The Internet Archive.
And here's the article about the origins of the story (which I may need to scan at a higher resolution). For now, click on the image then right click, save, and view through your normal application.