The Shroud is an especially stealthy vessel. Its hull is a further refinement of the normal Necron design, which is even harder to detect. As long as it is not crippled a Shroud will never activate orbital mines or grant the enemy bonuses to their Command checks if it is on special orders.
The Shroud’s superior sensors are capable of relaying information gleaned to the rest of the fleet. If a Necron fleet has any uncrippled Shrouds on the battlefield the whole fleet will get an extra +1 to their Command checks when any enemy vessel is on special orders.