The only mention of the Heavenly Host is in the third book of the Sin War novels, The Veiled Prophet. The Archangel Tyrael was given command over the Heavenly Host to lead them in obliterating Sanctuary. The Angels of the Host swooped down from the skies and struck their wrath on all who opposed them. It was at the same time that the ground split open and legions of Demons started spewing out from them.
Both the Angels and the Demons were forcibly banished back to their respective realms by Uldyssian, and the legendary Angiris Council descended to Sanctuary and voted to spare Sanctuary (though Imperius sought to have the Host finish what it had begun), whereupon Mephisto appears and makes a pact with them to leave the mortal realm untouched by either side.
Unlike demons, angels are disciplined fighters, and their unity allows them to defeat the sheer numbers of demons. Each Archangel, when present on the battlefield, fills their troops with the virtue they represent, which is especially important when the Great Evils attempt to demoralize the Heavenly Host with their own power (such as Diablo giving a Pandemonium Loop to Iskatu to instill terror in the hearts of angels).
Like the Demonic Legion, Heavenly Host is composed of many types of specialized warriors. So far the following types have been observed:
- Angelic Warriors are resilient, carry heavy white and golden armor, and usually carry massive Skywarden maces. They mostly fight on foot, and may operate or repair siege weapons.
- Angelic Scouts are unarmored and unarmed, carrying light white and golden robes, but adept in magic, able to operate siege weaponry, expel demonic corruption and project shields of force to protect allies.
- Angelic Lancers bear light silver plate armor and long pikes, which they use to strike from above, soaring upon the enemy and using their ability of flight to outmaneuver and outflank foes.
The hierarchy in the Host is similar to that in the Legion: while the five Aspects command their own forces, they have lieutenants (such as Izual or Urzael) as their second-in-command officers. Both Aspects and lieutenants may or may not be archangels, so this status apparently is not a rank in the Heavenly Host. It is possible that each of the five Aspects has their own types of troops. At least, Malthael's servants, even those seemingly unchanged after being transformed into Reapers, were very much different from the forces listed above.
Death Maidens' example shows that at least some regiments of female soldiers exist in the Host. It is not known if other forces are mixed or male only, but only male Warriors, Scouts and Lancers have been observed so far.
Angels, like demons, often utilize siege weapons, of which massive conduits of Light, lightning towers and ballistae have been observed. Unlike the Legion, angels may repair their siege weaponry in the field. Timeless Prisons are sometimes utilized to trap the demon champions in time, preventing them from being reborn in the Burning Hells.