Improved Comms
These upgrades take the form of long 'whip' aerials or other large aerial set-ups. A vehicle with improved comms can communicate with other Imperial Guard formations, such as nearby reserves or artillery support. To represent this, the improved comms allow the Imperial Guard player to re-roll one Reserves roll per turn, and to re-roll the dice when checking to see if an enemy unit or obstacle is hit by a preliminary bombardment.
Errata — Chapter Approved: Codex: Imperial Guard Q&A (v1.0): The 'one per army' restriction has been lifted, so you can field more than one Improved Comms vehicle — but no single dice roll may ever be re-rolled more than once. This means multiple Improved Comms let you re-roll more than one different failed Reserves roll per turn, but they have no additional (stacking) effect on the Preliminary Bombardment re-roll. An Improved Comms vehicle confers its benefit even while it is itself still in Reserve.