So far the forces of the Imperium have been brutalized at the hands of Chaos and Eldar pirates, but the Eldar do not discriminate and have manhandled the forces of Chaos as well. Damned pointy eared bastards!
That said the title most deadly ship goes to the Repulsive class Grand Cruiser the Betrayer. Holy crap this ship has single handedly killed or crippled a total of 13 cruisers with one salvo from its weapons batteries and lances. To top it off the ship has not been crippled once in the entire campaign.
I will be posting pics from the final two or three games sometime tomorrow.