All IFVs have a rapid pulse plasma "A" gun Pen 44 (+2 Autofire) - unless you went for the "single shot" Pen 54 version. Jess' ride has the point defence system with the VRF gauss slaved to that. It can carry just four troops.
The other "vanilla" IFVs retain the plasma gun but have the capacity to carry ten troops (instead of VRF gauss ammo).
The rapid pulse plasma gun is good against lightly armoured vehicles, bunker embrasures and all infantry but not starships (AV = 60).
If you kept plugging away at an AV 60 target with a Pen 54 weapon you'd eventually roll a six and get surface hits but not likely a kill.
However, the Pen 44 weapon is destructive enough that if you could get to "point blank" range and deliberately target certain ship components or vulnerable areas (cockpit windows, drive plates at the rear, sensor antennae, etc) you would surely degrade a ship's ability to effectively function and get a "mission kill". However, star ships are effectively super tanks and your IFVs don't want to be trading shots with starship lasers. One way to avoid this is to get close to the hull (or inside it) where the ship's turret weapons can't be brought to bear.
The weapons that you have that are capable of cracking ship's hulls are: breaching charges (zero range), the AT missile system mounted on one G Carrier and the launch/gunship's missile rack (three "full fat" ship to ship missiles).
