Grand cruisers are relics of a bygone age. Having been common in the Armada Imperialis during the Great Crusade and Horus Heresy, they were superseded by battlecruisers; however many sector fleets retain grand cruisers as second-line units, or mothballed as war reserves.
Resolute Blade is just such a ship. Her hull was laid down in the Jovian orbital shipyards in late M30. She then served in the 965th Expeditionary Fleet with the IV Legion, and particpated in the Solar War. After the Heresy, she was captured as a prize by the Imperial Fists during the Great Scouring, and presented to the Imperial Navy by Rogal Dorn himself.
Resolute Blade was assigned to the Vastus Sector in M33, as part of reinforcements sent from Kar Duniash during the first Ork incursion. She served on the front-line fleet in the Vastus sector from then until M37. She was then reassigned to the reserve fleet (based at Aquilius Prime), seeing sporadic action over the next four millenia, until the entire reserve fleet was activated in response to the disruption caused by the Great Rift.
Now, this ancient vessel prowls the Void once again, in service of the God Emperor, smiting His foes and defending His subjects as part of Battlefleet Vastus.