True it could be an Epoch or (whatever the UNSC Atlas) carrier type was, but it is unlikely to be a Punic. There may be other classes of carrier that we have yet to be formally introduced to, the Orion class being the latest.
We are told that the message Halsey sends to FLEETCOM is as follows:
“To Lord Hood at FLEETCOM requesting a large military force to be sent, explaining that the forerunner technology here might turn the tide of the war.” After receiving Cortanas message about the Covenant and Flood threat en route to Earth, Halsey adds the following information:
“Hood, you’ll have your hands full. Revise request, send elite strike team to recover technological assets from Onyx. Send Spartans.” The book clearly states that both the original and ‘additional message’ were transmitted. At the time the only threat faced by Halsey and the remaining personnel on Onyx were the sentinels, no Covenant fleet was present.
From what the Spartans receive we can gain slightly more insight into how Halsey worded her original message: “but the Dr Halseys text message arrived, explaining the discovery of new forerunner technologies and the possibility of using the to neutralise both the covenant and Flood threats.”
This shows that there was heavy emphasis on asset retrieval in the orders that Hood would give to Battle group that was formed for this mission.
Presumably he would have been given access to the same ONI report on Onyx that Kurt is given, which chronicles the history of the planet since its discovery by UNSC survey teams and it’s subsequent expunging from public record. It details the find of Forerunner ruins, and the excavations undertaken in the search for new technology. “The ruins are so extensive they would take several lifetimes to unearth it all. The entire world may be covered in similar ruins.” this coupled with the request from Halsey would have immediately made me think that ground deployment is necessary, if if it’s not in a combat role, but to assist with collection and removal of the ‘technologies’.
We are unfortunately never told what Admiral Patterson is informed and what his exact orders given by FLEETCOM are, but we do know what the crew of the Battlegroup’s Prowler were told. The Dusk, conducts a planetary scan of Onyx prior to the arrival of the rest of the Battlegroup. Lieutenant Commander Lash comments that “the fate of thousands of lives and eight other ships depend on this.” As far as I know official crew figures for Halberd destroyers, Marathon cruisers nor any of the carriers have been given. As for the Battlegroup composition, only 7 hours pass between FLEETCOM receiving the message, and the Battlegroup being destroyed. So in that small window, Hood had to find, brief and deploy the Battlegroup, using what was to hand at short notice, wasn’t otherwise engaged and being mindful of the grave threat that was en route to Earth. We know from Halo 3 that he is very relectant to send any ships to the Ark, and so based on this mindset, it is appropriate to believe he would send a minimal force, especially when there is no reported Covenant Naval threat.
LC Lash states his orders having been “Rendezvous with a Battlegroup under the command of Admiral Carl ‘Buster’ Patterson, provide assistance to the Spartan Team and hopefully obtain new technologies that would turn the tide of this war.” No where in those orders was fleet engagment mentioned, which follows on from no Covenant threat being reported to them.
As far as the Battle group is aware, they are to jump to Onyx, meet up with the Spartan Team and then load the technology onto the fleet to transport it back to earth. Therefore it follows that an anticipated ground deployment would have factored into the Battlegroup selection. Halberds and the Marathon would have been able to deploy Pelicans with ground forces and drop ODST’s, but are not stocked in the same way that a dedicated ground assault vessel would be. An Orion with its ‘cargo lighters’ (not sure if these are the ‘Pods’ from Halo Wars that can drop firebases down from orbit) and capacity for troop deployment on a large scale, be it via Albatross or Pelican dropships or even hitherto unknown means. It would also have specialists on board along with base building equipment, heavy lift gear, machinery and plant equipment not to mention technicians and engineers who would be needed to operate it.
I understand what you say about fleet operations when the Battlegroup arrived at Onyx, and that Admiral Patterson wouldn’t be stupid enough to try and engage the covenant and deploy and cover a ground operation, which is why I feel he so zealously engages and persues the covenant ships that are found. If he could win Naval and Air superiority, landing troops uncontested would allow for a quicker retrieval of the technology he is under the impression of needing to collect.
I think an Epoch, judging by its rules in game is much more of a dedicated warship, with more limited ground options, and that a Punic, whilst capable of performing the role, would never have been sent due to its strategic and combat multiplying abilities required in the defence of Earth.
I would like it if all the ships in the Halo Universe got more love, especially those that haven’t been seen in games or having their exploits detailed in the novels - eg Charon Fringate in Halo 3, Phoenix class Support Ship in Halo Wars, DDS in First Strike, ORS in Ghosts of Onyx, SDV in Hunters in the Dark etc… so I think this would be a perfect opportunity to ground the ‘new’ Orion Assault Carrier in the fiction.
Perhaps Grim can give his thoughts on the matter? Deep links anyone?
TL:DR I believe that the UNSC Stalingrad carrier from Ghosts of Onyx was an Orion Assault Carrier.