This comes up a lot and it's always a case of fans being very interested in one or two tiny references where no other information even exists.
And with good reason: Wing Commander II originally had a climactic scene in which the Concordia fires the phase transit cannon and against all odds destroys an attacking Fralthra. It had a bespoke animation and was ultimately cut for disk space. So all that survives in the base game beyond the ship having the gun in the engine is the reference in the manual to the ship having the special gun in the first place... one or two mentions explaning what it is in Joan's guide. Those fascinate fans because they touch on all kinds of cool ideas (mentioning the Sivar's weapon, having a big gun that the ship is based around, etc.)
But there's nothing beyond that. The game's script no longer talks about the gun, like the novels and every followup it treats the Concordia like a carrier. The cutscene animation got reused somewhat randomly at the end of Special Operations 2 (note the lack of setup or explanation and the fact that the Kilrathi ship doesn't even mention the design you see on screen!) and that's the end of what's known or seen about the PTC. But because Joan's is so tantalizing it comes up endlessly when fans talk spaceships.
The TCS Armageddon is referenced in Victory Streak but not as any particular class of ship, it's just home to one of the squadrons listed as winning a prize