Gladiator

Once per game, after completing its move, a vehicle with smoke launchers can trigger them (it doesn’t matter how far it moved). Place some cotton wool or other suitable marker on or around the vehicle to show it is obscured. The vehicle may not fire any of its weapons in the same turn as it used its smoke launchers, but will count as obscured in the next enemy Shooting phase, receiving a 4+ cover save. 

After the enemy’s Shooting phase, the smoke disperses with no further effect. Note that a vehicle may still use smoke launchers even if its crew are shaken or stunned.

It is worth pointing out that some armies might use different versions of smoke launchers, which have slightly different rules. As normal, the rules in the Codex take precedence.