Editing Imperial Navy (section)

=== Ship Size ===

No one is quite sure how big the ships really are. One story claims the Retribution-Class is a mere 3 kilometers long, while another says it is 9 kilometers and up to 20 kilometers.

Your best bet is Rogue Trader, although going by those figures, anything bigger than a cruiser has an average density around that of hydrogen... Everything after Rogue Trader became much larger, though, so this is likely inaccurate (though pretty big vessels anyway). Given the constant references to “city sized” weapon batteries and hangars, perhaps take Rogue Trader ship sizes and multiply ten or even a hundred. From a helpful poster on [http://www.heresy-online.net/forums/showthread.php?t=63267&page=2 Heresy-Online] we have this:

For the most accurate scale, look towards the Battlefleet Koronus Expansion, as it is more a stat/rule book than a story. That and previous consensi, as well as cross referencing with the Horus Heresy rulebooks by Forge World (which places Battleships at 8-12km) place Cruisers just above 5 kms, and Battleships in the mid 8s. Please note that most ships above the size of 8ish kilometers are either a unique modified/purpose built flagship or a ship of a small class that is not in widespread circulation. For a sense of scale the largest warship in the world is currently the US Navy's Ford Class Aircraft Carrier measuring in at 337 meters long or 0.337km making the USS Ford the size of a cannon. They have guns literally the length of an Aircraft carrier!

*Transports and other Attack Craft, typically rated for atmospheric operation; also includes ships designed to be boarding torpedoes.
**<1 kilometer. That's the small ones, there are super transports in 40k as well. (A [[thunderhawk]] would go here).
*Escorts are "small" ships, like the Cobra, designed to flank foes and operate in squads.
**1-2 kilometers.
**Heavy Frigates
**Frigates
**Corvettes
**Destroyers
**Freighters
*Light Cruiser, a smaller Cruiser.
**3-5 kilometers.
*Cruiser, the standard fighting vessel; every Imperial fleet has them.
**5-6 Kilometers.
*Battle Cruiser, a beefed up Cruiser; generally more 'modern' than a Grand Cruiser.
**6-7 kilometers.
*Grand Cruiser; pocket-sized Battleship, very old.
**7-8 kilometers.
*Battleship; the biggest of the lot, simply put.
**8-12 kilometers.
**Battleships
**Fleet Carriers

The Horus Heresy novel "Know No Fear" had this to say about ship sizes, taken from [http://archive.foolz.us/tg/thread/22848349/ /tg/] who quoted it from the book and written here is just the lengths and names of the ships, for simplicity and space:

*Macragge’s Honour. Twenty-six kilometers - Flagship
*Spirit of Konor. Seventeen kilometers - Battleship
*Antrodamicus. Twelve kilometers - Grand Cruiser
*Antipathy. Nine kilometers - Cruiser (note that the book said it had "six thousand lives" on board, which would be an absurdly small crew for its size by 40k or even 21st century standards, but it wasn't fully crewed at the time; maybe for an astartes or mechanicus vessel its a bit closer to reasonable but definite not for the Navy)
*Aegis of Occluda. Seven kilometers - Class unknown
*Gladius. Four kilometers - Escort
*Then there is the Abyss-class created by Lorgar that is said to match the Phalanx in size. He made three of them. In reality, they matched it in beam, but the Phalanx is round, so iut probably wasn't quite as big.