The Only chance I could see that is that the Luxury Liner could have been hijacked by pirates and turned into a makeshift combat vessel.
ex. A faction like the Gaians, they would not have the resources to build their own capital ships, but if they raided a liner they could take it and covert it to own use. You could also have a Prison Liner that was filled with prisoners, but they revolted and took it over. Now they are blowing up a lot of stuff.
These are both RP examples of how it could be used.