What is preliminary bombardment?
It's a way of winning a game before the first turn!
I remember the following from a rather large game I played back in the time of 3rd edition 40k. A large army of Orkz (commanded by me and 2 other players) made their last stand at a large fortified Ork city (which I believe was called Noo Orktun) against a large force of spacemarines. So it tuned out that orbiting imperial ships could hurl rocks down on the Ork City before the first turn. Preliminary bombardment apparently.
The battle went badly for the Orkz as one of the man-made meteorites hit a mob of War-Trukkz and their wreckage blocked the main gates of the city trapping the Ork's main strike force inside the city as the Emperor's Finest closed in on them. In the end only 1 bike squadron and a (then house rules) Deff-Kopta made it out side the city through a smaller side gate to deal any significant damage on the Genetically-Enhanced-Wonder-Warriors of humanity. The rest of the Orks remained trapped inside the city and were mercilessly gunned down one by one. Once again humanity some how won the hopeless struggle against the races with less special rules, lower armour saves and inferior wargear.
Ok ... bitter sarcasm aside, I believe an up-to-date version of the preliminary bombardment rules can be found here:
http://ca.games-workshop.com/Community/Hall_of_Heroes/images/HOHdownload/40kHOHspecialrules.pdf
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~The ravings of a single mad Goblin is bad enough, but such a power-hungry, malice-filled creature as Mortis can never hope to be understood~