The largest combat ship in the Hiigaran navy, the Battlecruiser has two long range Heavy Ion Beam turrets. These weapon systems allow the Battlecruiser to engage targets at extreme distances, making it a deadly foe for most capital class ships. A complement of four pulsar turrets and four kinetic burst cannons enable the Battlecruiser to engage strike craft intent on disabling key command, propulsion, or weapons subsystems. With proper frigate and corvette support, the Battlecruiser is the heavy-hitter of many fleet engagements.

"There is a new battlecruiser that is the mainstay of the Hiigaran fleet. While there are ships like the Battlecruiser, bristling with weapons, we've ensured that all ships are useful throughout the game. Bigger doesn't mean invulnerable. Fighters maybe be smaller and weaker, but their speed allows them to swoop past slower defenders and sneak in under the firing arcs of bigger ships. Without a proper balance of combined fleets, it is possible for a fighter squadron to disable even a Battlecruiser. Have a few Corvettes escorting the Battlecruiser and the situation would be far different." - Dan Irish, Executive Producer

This is the first Homeworld 2 vessel identified from a screenshot, appearing in a Relic website graphic that was leaked and then hushed up in November of 2001. It's a very, very large warship, and heavily armed.

Now that we can see the underside of the ship, the weapon picture becomes clear. The large turrets on the bow are twin Kinetic Burst Turrets; there are two more underneath port and starboard. The central turret topside is the heavy ion cannon; there is another underside. There are four pulsars, two each port/starboard. The only thing not accounted for in the weapons list above are the four box-like structures (two topside, two underside) that appeared to fire ion cannons in the 2002 PCGamer pics. Asked about these structures, Relic's Dan Irish replied: "These structures do not impart or control any abilities. Think of them as racing fins. The battlecruiser is, after all, a bit of a hot rod." 

The source images are somewhat dark, so I've modified and annotated an image with what is known of the weapon locations.