Advanced Space Crusade consisted of two parts - exploration and encouters. Exploration consisted of three paths of advance through a Tyranid ship. Your squads are represented by counters, and if you have a squad on the recon part of an advance, you turn an encounter card over for that advance path. That can lead to encounters, with squads in your force.
The encounter worked in a similar way to SH, but with more variety. You could take actions, giving you a number of APs. An advance gave you the standard number - 4 for Marines, for example - while a Charge gave you an additional 2 AP but you can only move and close assault. You can shoot using either a snap fire (1AP) or an aimed fire (uses almost one whole action).
Figures have an armour value, and the game uses D12. Shooting needs to roll over the armour value, and weapons have a modifier. It was an extremely elegant system, and I am still a HUGE fan!