I was recently perusing through the Hull classification symbol article, and realised that it was missing the SCS classification of the Halcyon-class cruisers, from the pre-release Transmissions that preceded Halo: Combat Evolved. I added them, but that is not what this post is about.
Bungie have used the Hull classification symbol system used by the current US Navy, but SCS is not found there. Neither is CFV, the HCS of the Phoenix-class colony ship, yet we have been able to extrapolate the newer HSC to potentially mean Cruiser-Carrier. Yet I find it odd that we haven't applied the same rationale to the Halcyon-class - perhaps, since its only found in the transmissions, people automatically assume its non-canon? We also find the CCS-classification in the Transmissions, which is confirmed canon, so obviously Bungie had at least some things planned out well ahead of the launch. Its interesting to speculate - which, in typical Specops fashion, I shall now do! The possible reason for its application are interesting, to say the least.
As I mentioned, the current system does not have an SCS classification, but it does have two other classifactions that may have bearing on the UNSC Pillar of Autumn. The first one is CS - scout cruiser. Given the Halciyon-class's pathetic armament and subsequent retirement from service, it may be logical to assume that it was intended for more of a scout and patrol niche than combat. The second classification is SC - cruiser submarine. The fact that the Halcyon-class ship has part of a submarine has interesting implications - given the nature of space warfare, Prowlers have taken over the traditional role given to submarines, using their stealth features to go undetected. It is possible that the Pillar of Autumn was equipped with stealth features during its refit? Is it likely that the Autumn was a Stealth Cruiser on a larger scale than the UNSC Point of No Return?
Given the nature of its original mission, I find it quite easy to believe. Entering Covenant territory, disabling and capturing a Covenant warship, and then jumping to the Covenant homeworld to capture the enemy leadership would require some major advantages, which the UNSC Navy's conventional forces simply do not have. The Autumn was equipped with a prototype MAC with triple the firepower, fifty CIWS turrets, thousands of Archer missiles, and a reactor far superior to any in service aboard other ships - while it isn't mentioned in the novels or games, it may have also been equipped with stealth ablative coating to further increase its chances of success. Given the existence of the destroyer-sized stealth cruiser Point of No Return, and the fact that UNSC technology has come along way since the 2530's, it may well be possible to "cloak" a warship the size of the autumn with stealth - the novels describe it as small for a Cruiser, hinting that it might be small enough for it to be applied.
It might also explain why the Covenant didn't just blow it out of the sky before it managed to crash-land on Halo - we know from The Fall of Reach, The Flood and Halo: CE that it managed to linger behind one of its moons before Covenant fighter recon pickets detected it. One would think that the Covenant would not need recon pickets, given the superiority of their sensor technology, but if Covenant sensors were having difficulty detecting the ship then obviously a Shipmaster would have to send in personnel to make visual identification.
The material obviously doesn't render the Autumn invisible, but optical scanners in space are inefficient. Considering the sheer distances between ships, and the speeds fought at, they may even be redundant in space combat. At a thousand kilometers, in a three-dimensional battlespace, against the backdrop of inky blackness and pinpricks of stars, with the usual debris found in a planetary system, scanners would be hard pressed to separate an object of warship-like dimensions from the myriad of other junk by sight alone. Rather, sensors such as Radar, LDAR or Masers would be the more reliable sensors used and favoured, and these can be confused, refracted and deflected, and absorbed.
I may still be way off, or my reasoning may be flawed. But even if I am wrong, its still interesting to try and draw information from the barest of information.