Was just commenting on the related topic...and this one occurred to me! The Imperium has a handful of mobile space fortresses that I'm aware of: The Dark Angel's Rock, the Imperial Fists' Phalanx, the Fire Hawks' Rapturous Rex and the Ramilles Class Star Fort. Does anyone want to hazard a guess at the sizes of these monsters?

They seem to have a slightly less reliable warp safety record than smaller vessels: the Imperium seems to have lost a lot of Ramiles Class stations over the years, and the Rapturous Rex was lost in the warp alongside the entire Fire Hawks chapter...

This suggests to me that there is a sort of "upper size limit" for safe warp-capable space vessel transport. What do you think?

It may just be that the losses of large war capable fortresses are more notable - a loss of a Frigate to a squadron commander is painful, the loss of Ramilies may be major blow to Sector Command. The loss of the noted Space Marine fortresses would be near death blows to whole Chapters........

I personally don't think they are any more likely to succumb - in fact probably mroe resiliant -otherwise its probably too many eggs in one basket?

Or maybe larger ships have more unique gellar fields/warp engines that get harder to maintain as Imperial technological knowledge has atrophied, and this makes them more unreliable compared to simpler, mass produced models like frigates, cruisers etc? Just a thought...

I agree with Da Boss, the really big ships are notable because their losses are always going to be significant events, not because they are more likely. Even casual students of WWII history will know of the Bismark or Yamato, but the losses of smaller classes of ship just show up on tables of figures which only serious studies wikll pay attention to.

For me, the upper limit on Imperial starship size has been more an economic thing. Cobra class destroyers can probably be built by any shipyard and take several decades to finish. A Battleship will likely take a major shipyard based in a Forge World centuries to build. It's possible that not every Sector has a facility capable of building Battleships. So how many places in the Imperium will be able to build something even bigger, and how long would it take them.

Historically, navies would rely on big ships of the line in major battles. But these battles were the exception, not the rule, and most of a fleet would be made of smaller classes because there was no way to make a navy big enough to be everywhere it was needed if every ship was the biggest and best possible. The Imperium seems to follow this trend. I can't recall where it was stated, but I definitely remember reading that smaller ships often have a better Captain and/or crew. Smaller ships will see action more often, and not being as prestigious an assignment are more likely to have the bridge officers chosen for ability rather than political connections.

I also feel that there's going to be a point of diminishing returns regarding how big and powerful a ship is compared to how much it costs to build in time and resoruces. A 30-kilometre-long Superdreadnought packed with Archeortech might be able to take on an entire Sector Fleet, but if it costs the same to build as two Sector Fleets- well, it's just not going to be made.

So- bigger ships can happen, but I'd think long and hard about why they were made. A derelict from the Dark Age of Technology that was recovered and refitted? One insane Sector Commander's obsession which he beggared his Sector to build, and which was the only thing to escape when the Orks overran his shambolic realm after his death?

They need a backstory just as epic as the Dark Angels' fortress. Otherwise, why didn't the Imperial Navy just order a larger number of smaller ships?

I agree with Tantavalist. HUGE ships tend to be strongpoints for a fleet, but the costs are in most cases far bigger than the trade-offs.

I don't have my books with me but I seem to recall the Rock is the largest human warp 'ship'. But how it travels is a mystery no? I thought it was all lost technology.

Space Hulks bear a mention, they're asteroid sized and enter the warp though dozens of warp engines firing at once abd cab't be steered.

Craftworlds might be the biggest space vessals, have they ever been given a size? But of course they use the webway.

The biggest (sort of) human ship I can think of is Abaddon's Planet Killer but that was also mysterious lost/chaos tech.

I think the Emperor Class battleship is the largest the Imperium can reliably build.

But as in the real world, there might be larger freighters and tankers which are much cheaper to build than warships and might be needed to supply hive worlds. IIRC the largest ship ever build in the real world was an oil tanker (it was damaged during the Gulf War and eventually scrapped). The largest ships currently being built are container ships and tankers. They would be made even larger than they are but economic reasons cap them at the size of the Panama Canal (which is now being widened for that reason).

Kid Kyoto said:

If i remember correctly, it`s not entirely clear, how or why space hulks enter or leave the warp on their own. It`s a bit different with ork-owned hulks, for there lots of mekz just do what comes to their mind.

Craftworlds don`t even enter the warp, the just kind of "drift". The "smaller" Eldar vessels use the webway.

The light of the Emperor is massive, way bigger then most capital if the description is correct and an archeotech ship.

I don't remember where they talk about a freaking huge transport ship the Slaugther House that would be extremely big but just a transport.

I am inclined to believe that there isn't much in the way of a upper limit on ship size, just a practical one. I just figure that the largest Imperial ships are dedicated towards trade rather than military or exploration duties. I huge warship would be an enormous target, and while it might be difficult to disable once it is down that is going to have a big demoralizing effect on its escort ships. Whereas a giant cargo hauler is absolutely required to keep Hive and Forge worlds supplied.

I recall reading about a transport ship that each cargo hold was enough to hold entire armies, and even when empty the far side of the hold was too distant to be seen. I though that Craftworld did enter the webway, but since the Fall of the Eldar it has become so damaged that only a few gates are large enough for them to access.

More than likely the biggest of functional capitol ships would top out in the 10 km length, some more ancient ships in the 12-15 km range.

The Phalanx would be enormous. Hundreds, if not over a thousand km in diameter. The Rock would probably be much smaller than the Phalanx, but still dwarfing most other ships.

I think the upper limit on ship size is less a restriction on how big before they can't be transported through the warp reliably (although I have my thoughts on the matter- see below), or even how big before the monetary cost outweighs the usefulness, but simply a reflection that the bigger something is, the less maneuverable it'll be.

Combine that with the flexibility of shoving the same amount of weaponry and engines in several hulls rather than one big one, and is simply isn't particularly smart to go with big ships without massive escort fleets to screen them (look at the Planet Killer- definitely one of the larger Battleship-sized ships out there, if not up in the Dreadnought weight. What killed it? A squadron of Cobra Destroyers who were nimble enough to stay out of her fire arcs and bombard her with more torpedoes than you can shake a stick at).

(My own theory is whenever someone's pet ship design grows too big to be practically maneuvered, they strip the drive tubes, replace them with docking bays, maybe some weapons components and call it a space station.)

Of course, when you want to move something that big and it doesn't have it's own drive, you have to start grabbing tugs. And 40k being the kind of setting that it is, said tugs probably need to be able to defend themselves (warning bells should start ringing soon- it's typical MilBu logic ahead). And since warships should have a load of spare power and acceleration in hand, and the capability to defend themselves, why not use warships as tugs?
The problem is, a tug has some rather specialised design requirements- you can't just tie a bungee cord through the bumper and gun the engine. It has to have plenty of engine power to spare, be capable of transferring delta-v along the desired axis even though it is virtually never going to be thrusting through the centre of mass and (and this is a biggie), have a structural frame capable of withstanding massive torsion and shear stresses.
Even with typical Imperial over-engineering, that's not what a warship is built to be able to do.
And yet, when they want to move a Ramilles around, what do they get to act as tugs? Emperor-class BBVs.

Most of those design parameters mentioned just now were with regards to travelling in real space (pulling it from one orbit to the next), but they should hold true for towing stuff through the warp. Only there, there's another requirement- between the tugs and towed, there should be sufficiently expansive Geller Field coverage to protect every part of all ships, towed stations and whatever is being used to attach the towed to the various tugs.

Now while it is possible that some of the oldest and most advanced big-ass ships have a single Geller Field generator capable of projecting and protecting a much larger volume (which has it's own problems, thanks to loss of knowledge over the millennia), I suspect it's much more likely that the larger vessels (possibly even from as small as a cruiser) use a number of separate Geller Field generators as part of the same component, arrayed so that their fields overlap and interlock.
If that is so, then the design starts to fall afoul of the "Airplane Rule"- the more parts there are, the more things can go wrong. All it would take (potentially) for a ship to wind up lost in the warp is for one of those generators to blow a fuse, or short itself out and suddenly you've got part of the ship exposed to the warp and oh, dear; the repair crews just got eaten by daemons...

I could have sworn I saw in either one of the Dark Heresy books, or in the Rogue trader core book that some of the chartist, and or cargo vessels can actually dwarf most imperial military ships. That probably means they're also about battleship size though.

Most of the warp capable gigantors of the imperium really don't seem to do much in the way of warp travel. Either because it's dangerous to move them that way (Fire hawks anyone?), or because coasting in the void between the stars is more advantageous for your deathstar (The Rock and craftworlds). Why bother moving the priceless relic when you have a fleet of normal ships that are easier to replace?

THere's also the issue with bringing a moon sized battlestation into a star system. If it's that huge it might cause all manner of shenanigans on any celestial bodies it comes near. Things like Floods, hurricanes, etc.

But to answer the original question. The older they are, the better chances of them being bigger than anything else out there but the upper limit seems to be the size of a small moon. Unless it involves orks, then all bets are off. But anything huge and imperial that's warp capable should be very old, and either a lost legend to be found, or under control of a very powerful faction.

One thing to consider in size of a warp capable ship is the amount of people needed to operate it. Now this may not seem important to warp travel at first, but more people are going to be a bigger draw to warp entities. Thats bound to cause problems

In my campaign i've introduced "Greatholds" massive cargo vessels used to transport really, really big stuff, like titan legions, or pre-fabricated space defenses, monitor ships and even disassembled space stations. They don't do trade runs as such, more, they are owned by massively powerful groups like the Admech and the Navy and are used specifically for certain missions. My PCs swung a deal with the admech to get 4 system monitor ships and a bunch of defense platforms delivered to a system they own, a great hold is the only vessel capable of that.

I'd also see them used in truly huge wars to move the kind of troops and equipment you'd need for the big, hive world type wars. A greathold could move literally millions of troops in one go along with entire regiments of armour, aircraft, etc. Of course, its something you'd want to protect well.

I imagined them being larger than a battleship, about 10km long and most of their bulk being vast open cargo holds.

Gribble_the_Munchkin said:

These are a very nice idea, they remind me of the descriptions in Titanicus of the vessels that bring a Titan legion to battle.

Do you have any stats for them?

DW

No stats yet as they've only appeared in my game as a means to move some monitor vessels my PCs bought. Seemed to me like there was a niche that would need to be filled by some truly vast transports.

If you wanna make stats i'd suggest low to middling armour, hull points around a cruisers and maybe a pair of weapon systems, both dorsal for protection. Lots of space but have most of it pre-dedicated to a bunch of super massive cargoholds.

Battle for the Abyss (HH book) has the "largest imperial ship on record" supposedly, though I don't think you could call it technically imperial. Ranked after that would be the Phalanx, which was the Emperor's personal flagship until he gave it to Rogal Dorn as a gift. The Rock (The Dark Angels flying fortress) can travel, but it's more of a mobile space station and less of a ship. An Imperial Ship can really get as large as they want to make it, the problem becomes a matter of time. It takes something like 50 years to make something the size of a cobra destroyer and over a century for something like a lunar, more for a battleship. You could start making a ship the size of four battleships put together, but it'd probably take a millenium to build.

Actually, a hive world (not even a dedicated forge world for shipbuilding) can build a Lunar class in under a decade (3 years, assuming they concentrate the resources of the entire planet into building it or supporting it's construction).

Alasseo said:

Where do you get this information from?

I recall reading that the reason the Lunar class was becoming the standard for the Imperial Navy was that it's hull was simpler to construct and worlds otherwise incapable of building Cruiser-class hulls could manufacture them. What I don't recall reading anywhere is that it takes less than a decade to do so. Thirty years would be pushing it given the description of how long ship building takes, three? Doesn't seem likely.

Kid Kyoto said:

Trivia time!

I think you are referring to the Panamax size, but there is actually a larger size (Cape size) which can't fit through any channels, and have to go around the capes instead.

Tantavalist said:

It was in one of the background bits for Battlefleet Gothic. Although, having re-read it just now (to provide evidence), it seems I remembered it wrongly- the Lunar-class vessel His Divine Majesty's Ship Lord Daros was built by the feral world of Unloth in 11 years (BfG BBB, p 110). I'm fairly certain I've seen an estimate of 3 years for a hive world elsewhere, but since it wasn't the reference I thought it was I've no idea where. It should certainly be possible to do so in under a decade though, given the example of the Lord Daros.

Tantavalist said:

Surely it depends on the world constructing it? One imagines some massive forge worlds that specialise in churning out spacecraft would be capable of putting together a ship faster than some frontier sector hive world. I'm not suggesting constructing a ship isn't a colossal undertaking - it self evidently is - but in parts of the Imperium the infrastructure will be there to put these things together pretty quick.

BrotherHostower said:

Phalanx is small moon size = much bigger than Abyss and was not gifted to Dorn by the Emperor. It was Rogal's from the start and he offered the ship to the Emperor as a gift. The Emperor declined and willed that Dorn use the ship as Primarch of Imperial Fist.

It was gifted insofar as the Emperor didn't take it from Dorn when it was offered.

ItsUncertainWho said:

Someone is trying to suck up to the Eclesiarchy! The Lord Giveth and taketh not!