When shooting, a unit of vehicles fires all of its available weaponry at a single opposing unit. When a unit of vehicles is fired at any hits are distributed evenly amongst the vehicles, starting with the nearest vehicle model. No vehicle takes more than one hit until all of the vehicles in the unit have taken one hit each. Once the hits have been distributed roll to penetrate armour and make any damage rolls as appropriate.
EXAMPLE: An Ork Trukk fires its big shoota at a squadron of two Vypers, and scores two hits. This is divided between the Vypers, one hit on each, rather than both hits on a single Vyper.