This potent protective artefact is said to have been worn by Lion El' Jonson himself. It takes the form of a winged Space Marine helmet and is carried by a Helmet Bearer who is one of a strange race of creatures which inhabit the Rock and are known simply as the Watchers in the Dark. Whenever the character moves, simply place the Helmet Bearer within 2" of his final location, even if the character was teleported or moved by some other extraordinary means. The Watcher has a unique, powerful psychic talent protecting it from all forms of attack, so it can never be harmed in any way, under any circumstances. However, it cannot attack in any way either. If the character is killed or removed from battle, the Helmet Bearer is also removed, but will reappear if the character later returns.
Built into the helmet is a device that can be used to create a protective force field. This has the effect of providing any model (friend or foe) within 3" of the Helmet Bearer with a 4+ invulnerable save against any shooting attacks. Note that the helmet does not need to be worn in order to be used, and also note that the save may be taken instead of another save, not as well as it.
Errata — Chapter Approved: Codex: Dark Angels Q&A (v2.0): The Lion Helm's protective effect does not extend to vehicles.