The title seems to be a paradox in itself as you would not associate angels with being 'terrible'.
In stanza one it shows how we view was as heroic, with the war medals having 'pretty coloured ribbons' suggests how war is not valued as much when it's over and all we care about is the medals.
The 'meat snatching birds' sound like that the birds are waiting for the soldiers to die. The simile 'circle around and around like a carousel' gives the image of the birds continuously circling, waiting for the soldiers to die before they swoop in and eat them. Alternatively, 'horses to bolt' and 'birds to rise' could also be interpreted that warfare scares all life away, even 'meat snatching birds' - something which sounds sinister and cruel.
The second stanza shows how the soldiers became ruthless and 'bloodthirsty'. This image sounds quite animalistic, like they've lost their morality.
'To steal the muskets of the dead' makes the soldiers become 'stealthily visible' - paradox. Could show because their now invisible they don't have to hide who they really are.
'Bold and bloodthirsty, true facsimiles of men' could suggest that they were like this before they died as they are an exact copy and they haven't changed yet being an angel has awakened their bloodthirsty nature. Could be that they had to hide it when they were alive but can show it now their dead.
'Than was healthy' suggests that his father is no longer healthy and that the war has left him weak.