Vehicles don't fight in close combat as such although they can be attacked by enemy troops. However, heavy vehicles like tanks can break through enemy positions, scattering units and possibly forcing them to fall back – this kind of attack is called Tank Shock and is described below. Dreadnoughts, giant humanoid walking machines designed to spearhead assaults, and other walkers fight in close combat the same way as troops do.
Vehicles In An Assault
Source: Core Rulebook 3E, p. 89
Vehicles don't fight in close combat as such, though tanks can Tank Shock enemy units and Dreadnoughts and other walkers fight in close combat like troops.