Portcullis

The Portcullis was a type of super-heavy, mono-tracked vehicle once used by the Legiones Astartes during the Great Crusade and Horus Heresy eras of the early 31st Millennium. The Portcullis featured powerful energy-shield generators, similar to Void Shields, and the Portcullis tanks of the Dark Angels Legion in-particular featured an advanced design known only to the 1st Legion. These vehicles would be used as mobile shield generators to protect allied infantry and armour form enemy ranged fire.

Trivia
A "Portcullis" is a strong, heavy grating that slides up and down upon vertical grooves and was used during medieval times to block a gateway to a fortress or a town.