When you want to fire at a vehicle treat it like any other unit. One of your units can choose it as a target and must direct all of its shooting at it. Often this means that some of their weapons can't damage it, so assume that the other members of the squad are giving covering fire, bringing forward ammunition for heavy weapons or simply keeping their heads down!
NOTE: Only terrain & vehicles block line of sight to a vehicle.
When placing a Blast marker or large Blast marker to attack an enemy vehicle, the circle at the centre of the marker must initially be over the vehicle, or one of the vehicles if the target is a unit of vehicles. It may be that models from other units are under the Blast marker and these are also attacked. Flame templates should be placed so as much of the template as possible is over the enemy vehicle without also touching a friendly model.
Roll to hit against vehicles in the same way as against troops. If any hits are scored you then roll for each to see if they penetrate the vehicle's Armour Value, as explained later.
Vehicles can normally be targeted even if they are in close combat with friendly models. Vehicles which have a Weapon Skill characteristic (normally walkers) may not be, however.
All vehicles even partially under a Blast marker, large Blast marker or flame template are hit. However, if the hole in the middle of a Blast marker or large Blast marker is not over the vehicle then the Strength of the attacking weapon is halved (round fractions up) when working out whether the shot penetrates the vehicle's armour.
Designer's Note: Against large model vehicles, ordnance shots had a tendency never to miss and it has become the norm to place ordnance Blast markers so that they touch several targets. This will now only be worthwhile against the lightest targets so shooting straight at the target is a good thing.