I know a considerable amount about the British military. I know that it has always been comparatively more humane than almost any other in the world, as well as more successful - to the despair of its opponents.
As for the artistic merit of the song, the lyrics at least are a typical example of the teary, bathetic bleating that gives folk music a bad name. The facility with which lies are made up about particular incidents in history reflects the banality of this kind of sentimental, drippy ballad - I could write a dozen a week.