From Warhammer 40k - Lexicanum
The Serpent's Coil was a 013.M31 to 014.M31 Horus Heresy campaign, that the Alpha Legion waged to hinder the Loyalists' forces approaching from the Galaxy's galactic east.
Despite defying Warmaster Horus' orders against undertaking the campaign, the Serpent's Coil met with success. In order to prevent further losses of vital reinforcements, the Primarch Guilliman's Ultramarines battle fleet was ultimately forced to intervene against the Alpha Legion's attacks. This led to his Legion being unable to reach Terra, before it was invaded by Horus' forces.
- 1: Horus Heresy Website: Explore the Galaxy - The Serpent's Coil (Posted on 02/06/22) (Last accessed on 2 June 22)