: In my opinion what we're looking at here is references from a book who's
: material has largely either been superseded explicitly (Elites fighting
: throughout the entire Covenant war) or implicitly (like with the idea of
: UNSC ships having rotating sections for gravity which has never being
: mentioned ever again) and sizes and dimensions from a game (Halo 2) who's
: development was later revealed to be extremely rocky.

: I like The Fall of Reach and I like Halo 2, but I very nearly don't consider
: the former canon anymore except for the parts that are supported by later
: fiction (Cody Miller, eat your heart out! :P) and am always cautious when
: relying on anything but the most direct facts from the later. Measuring in
: game ship sizes would not count as a most direct fact for instance.

: The Autumn class are from where again? The cutscenes in Halo 4? The long
: version of the Halo 4 commercial with the christening of the UNSC
: Infinity? You may have a perfectly reasonable answer for this, but how do
: we even know how big those ships are or that they are heavy cruisers? If I
: (being the less detail oriented person that I am) tried to classify them
: I'd probably come up with the idea that they're all Halcyon class, just
: some that were refurbished from storage on some world not hit by the
: Covenant.

: In any case I'd lament the fact that 343i chose to make a ship so visually
: similar to the Pillar of Autumn. If we go by Halo Wars the Autumn (and
: thus Halcyon class) is something around a forty year old design at best.
: Trying to explain and classify things that seem so similar is hard, and
: maybe a bit of ship design diversity would be good for Halo.

: I believe in making up fiction to best fit what we have, and in this case our
: most solid facts tell us that the Pillar of Autumn (seen in Halo CE,
: various books, and Halo Reach) is a Halcyon class cruiser. Everything
: else, as far as I know, is less concrete and thus has to bend so as to fit
: around what we know about the Pillar of Autumn.

What I mentioned are the facts about the Autumn but that conflicting info comes into play.

Yes, the Autumn's info above is from the Fall of Reach novel, but it's from the "Definitive"-latest-approved-by-343i version of the novel updated in 2010.

The Marathon-class is the one from Halo 2.

The Autumn-class and it's length are from the new Visual Guide and is seen also at the end of the Forward Unto Dawn series final shot.

This is all "official" info. But as I said, the only thing that makes it all play nice is that the Pillar of Autumn looks and is sized like the Halo 1 version and not either the Reach or Anniversary edition (both of which are minorly different from one another!)