Some vehicles are not fully enclosed but expose their crews to a hostile universe. There are many reasons for this: It may be to give reconnaissance units a good field of vision, to make embarking and disembarking easier, or it may simply be impractical to enclose the crew. In the case of Imperial Guard artillery vehicles, such as the Basilisk, for example, the crew require plenty of space to load and fire the enormous Earthshaker cannon. This aside, it is mostly smaller vehicles that are open topped, such as Ork buggies and trukks.
While crews and embarked troops on open-topped vehicles have more freedom of movement and much better arcs of vision, the lack of an enclosed cabin inevitably means that they, and their vehicle, are more vulnerable to incoming fire.
Some vehicles are more vulnerable to damage than others because of their lightweight construction and the fact that their crew is exposed to enemy fire. A typical example of an open-topped vehicle is an Ork Wartrak or War Buggy. Whenever a Damage roll (glancing or penetrating) is made against an open-topped vehicle, add +1 to the Damage result.
Template and Blast marker weapons are particularly dangerous to open-topped vehicles because their crewmen, wheels, engines and other components are not protected against the flames and shrapnel. To represent this, template and Blast marker weapons cause double the normal number of hits against open topped vehicles (i.e., two hits instead of one).
Obscured Targets and Glancing Hits. A vehicle moving especially fast or behind cover, whether natural or artificially generated, will be harder to destroy. Remember that any weapon firing at a vehicle must pick its target spot carefully if it is to be successful and an obscured target denies the opportunity. The exact circumstances are detailed below.