You can also, link, split and combine firepower, meaning you roll more dice at one go. Generally you get hits on a 4, 5, or 6. The 6 counts as two hits, and allows you to roll another D6, generating potentially more hits. If you luck is with you can sometimes generate a lot of hits from only a few AD.
This is called the Exploding D6 mechanic. Its what can alter whole games regardless of how bad things are going for you!
The Critical Hit table is nasty, rolling 2D6 and consulting the chart, with a double 1 or double 6 being equally evil! You can also end up with results that Cripple your Ships, Movement, Systems, Weapons, Marines! All in all you want to hope the opponent doesn’t get something nasty as it can totally alter the game!