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Even without moving parts, extreme cold will have an effect. Parts become brittle, focussing arrays shift out of alignment and power pack charge levels could be affected as battery chemical reactions are slowed down.

Tyranids in sub-zero conditions often spawn more raveners, trygon and similar tunneling beasts to avoid the weather entirely. They also tend to forgo flyers as they're not cost effective in a freezing storm, and rippers only appear in the consumption rather than subdual phase as they generally don't find enough biomass to justify their creation until the fighting stops.

Source: deathwatch RPG source books.

Was just flicking through old codices and came across the lore snippet for the Vostroyan "Old Irascibles", who sacrificed themselves to destroy a splinter Tyranid fleet. The regiment destroyed approximately 85% of the remaining tyranid force when they commited suicide by blowing the reactors at the core of the city they were defending. It explicitly notes that the remaining 'nid organisms starved to death in the harsh winter that followed- presumably Tyranids run out of energy to fuel themselves quicker in cold climates. The energy obtainable from sunlight would be weak on a wintery world, and likely weaker still after a large nuclear reactor detonation, and most of the remaining biomass atomically incinerated itself at the onset of winter.

Whilst this episode stopped the hive fleet from progressing further, I am sure there are still dangerous Tyranid lifeforms in hibernation on the world that could ultimately reactivate the fleet if enough unwitting fresh biomass falls prey whilst scavenging/investigating.

To be honest I always found those lore snippets silly. I mean congrats you destroyed a city, which does nothing about the Hive Ships in orbit that can just send another wave, and of course Tyranid invasions are planet wide events in which the destruction of an individual city shouldn't really matter.

I rationalize them away with the snippets leaving out important information like Imperial naval assest that dealt with the Hive Ships and allies forces that helped at the planet scale.

Kinda like how most depictions of Macragge focus on tbe Ultramarines even though there were billions of Guardsmen, a Titan Legions and a Segmentum battlefleet present that kinda should overshadow a thousand Marines.

If the hive ships in orbit were low on biomass then ground forces being destroyed in a large scale could mean that the invasion fails and the hive ship is forced to retreat to better/easier feeding grounds to replenish its stores. This might be preferable to the hive ship eating itself (thus weakening itself) to continue a ground war that its ultimately losing.

Not every Tyranid invasion is the full force of a tendril; many times you get splinter fleets breaking off the main force which will strike other worlds.



This is indeed without considering orbital defences and such which will also take their toll on a hive fleet.

 Tyran wrote:
To be honest I always found those lore snippets silly.

Yeah it is silly. It's Warhammer and more specifically the Imperium. Sacrificing an entire Regiment of Guardsmen and a Hive City to stop a Tyranid tendril is just the sort of dumb nonsense that also usually has no real lasting effect that makes the Imperium what it is.

That example is how you deal with Hive Fleets overall - with the Shadow In The Warp making an on paper “simple” approach pretty tricky.

In standard warfare, provided the Tyranids win, they’ve not really lost much, as everything gets recycled and remade.

But there is a tipping point of resources expended and resources gathered. If the fleet itself is driven off before it can start feeding, it’s a net loss in resources. This diminishes its effectiveness the next time it tries to grab a snack. If it suffers a handful of such defeats in a row, it’s curtains.

We see this writ large in the Kryptman Gambit, which wasn’t just detonating worlds - but doing so at the right time, namely after the Hive Fleets had expended resources planetside. And….it worked, at last in the short term.

Hence I’m confident an Imperium in which the Heresy never happened would’ve been relatively well placed to deal with the Hive Fleets. After Ullanor Orks were at least largely contained. Eldar would’ve been next up on the extinction bill. Tau never would’ve grown out their infancy.

The main problem with fighting Tyranids is a lack of understanding of the full threat level. You don't know if those hundreds of worlds you sacrifice to stop a tendril have been worth the sacrifice or not because in the medium to long term you've no idea how important that tendril of hive ships is to the Tyranid race.


It could be a major fleet that's the backbone of an invasion and defeating it is going to cripple them for generations. Or it could nothing more than an advanced scouting force, the loss of which changes nothing; or it could be the loss of it makes the Tyranids pay even more attention and the more of them you kill the more they will send etc...

You've also no sense of timescales. Sacrificing whole worlds which can later be restored to use is fine; but if the next Hive fleet is coming next week its not a tactic which works; however if the next fleet might be 5 thousand years away then these burn strategies work.



This is a real problem with dealing with Tyranids, there really is zero concept of the overall scale of what you are dealing with. It makes sacrificial and retreating tactics much harder to justify and defend when you've no real idea how they impact anything but the fleet right in front of you

That may depend on just how handily the initial attack is repulsed.

For purely argument’s sake, let’s consider The Perfect Fortress World, with no GSC presence at all.

Orbital stations festooned with well maintained, accurate and powerful defences.

The initial tendril or scout fleet takes an absolute pasting, the Perfectly Lead Perfect Forces Perfectly Performing, annihilating the Hive Ships before they get close enough to reliably unleash their gribblies planetside.

If it is just the tip of a tendril, the Hive Mind may decide to send a greater force, because this Prey That Fights is particularly Fighty.

But again I think there will be a tipping point in expenditure where the Hive Fleet just gives up and sods off elsewhere, in search of a tastier snack.

If that’s right? It may be linked to whatever capacity the Hive Mind has for analysing likely biomass on a given world. Something like a fully functional Necron Tomb World is going to offer radically different resources for consumption to a Maiden World.

Sure Tyranids can and do extract minerals, so there is something to consume on a Tomb World. But once it figures out it’s expended forces are being disintegrated, leaving nothing to be reasorbed following victory? The calculus may simply lead to “sod you then, we’re going to McDonalds”.

Going really out there into “I’ve no way to support this” realms? It may also include the likelihood of getting new strains of DNA to consider and consume.

 Overread wrote:
If the hive ships in orbit were low on biomass then ground forces being destroyed in a large scale could mean that the invasion fails and the hive ship is forced to retreat to better/easier feeding grounds to replenish its stores. This might be preferable to the hive ship eating itself (thus weakening itself) to continue a ground war that its ultimately losing.

Not every Tyranid invasion is the full force of a tendril; many times you get splinter fleets breaking off the main force which will strike other worlds.

This is indeed without considering orbital defences and such which will also take their toll on a hive fleet.

My issue is that if you take the lore snippet as the totality of the information, then the Hive Ship retreating doesn't really make sense because the defenders also just blew up themselves, leaving the planet defenseless.

For it to work it needs offscreen orbital defenses or something else that keeps protecting the planet.

 Mad Doc Grotsnik wrote:
That may depend on just how handily the initial attack is repulsed.

For purely argument’s sake, let’s consider The Perfect Fortress World, with no GSC presence at all.

Orbital stations festooned with well maintained, accurate and powerful defences.

The initial tendril or scout fleet takes an absolute pasting, the Perfectly Lead Perfect Forces Perfectly Performing, annihilating the Hive Ships before they get close enough to reliably unleash their gribblies planetside.

If it is just the tip of a tendril, the Hive Mind may decide to send a greater force, because this Prey That Fights is particularly Fighty.

But again I think there will be a tipping point in expenditure where the Hive Fleet just gives up and sods off elsewhere, in search of a tastier snack.

If that’s right? It may be linked to whatever capacity the Hive Mind has for analysing likely biomass on a given world. Something like a fully functional Necron Tomb World is going to offer radically different resources for consumption to a Maiden World.

Sure Tyranids can and do extract minerals, so there is something to consume on a Tomb World. But once it figures out it’s expended forces are being disintegrated, leaving nothing to be reasorbed following victory? The calculus may simply lead to “sod you then, we’re going to McDonalds”.

Going really out there into “I’ve no way to support this” realms? It may also include the likelihood of getting new strains of DNA to consider and consume.

It isn't just the biomass calculus, there is also the long term, larger scale warzone calculus. The Perfect Fortress World may not be a particularly tasty snack, but its destruction could very well cripple the prey's capability to defend the nearby systems, maybe even whole sectors.

But the really frightening and problematic thing is that it is only the Hive Mind who is really aware of the numbers involved. Humanity has no truly reliable way of estimating a hive tendril's strength, which means humanity is stuck in a mostly reactive strategy. And reactive strategies is how you lose wars.

 Mad Doc Grotsnik wrote:

We see this writ large in the Kryptman Gambit, which wasn’t just detonating worlds - but doing so at the right time, namely after the Hive Fleets had expended resources planetside. And….it worked, at last in the short term.

Very debatable, while it slowed down Leviathan it also led to the destruction of Gryphonne IV, aka a very important Forge World, and the whole mess in Octarius.

There is a very good reason why Kryptman was excommunicated and is currently being hunted down by the Inquisition.

Kryptman’s plan was the best they had at the time though. A non-Heresied Imperium could’ve done it far better, starve and strike, rinse and repeat.

But to drag us dangerously back On Topic.

Extreme of temperature just aren’t the issue many might think.

Anything in Power Armour is good to go. It can operate in space, so any cold environment isn’t going to be much of a hindrance (though how they avoid sinking into snow is…..handwavium)

Imperial Guard? Regiments have Cold Weather Gear available, and given the ubiquity of their vehicles, which is why the Guard favour them in the first place, we can reasonably infer that extends to extreme weather modifications to engines, drive and weapons.

Orks tend to be tough enough to not need any wussy extra protection (ref Ciaphas Cain books).

Nids? Even if they get frozen? They can thaw out and get back to killing (not just Old One Eye)

Eldar? Again we can reasonably infer such an advanced species will have suitable equipment, or their basic equipment is natty enough to be self warming/cooling as required.

I’m really not seeing any species that doesn’t have relatively straight forward ways of remaining Battle ready in even the most extreme of weather environs.

It’s Deathworlds, Plagues and Toxins that tend to be the real bugger.

Orks tend to just tough it out, maybe relying on squig pelts to act as windbreaker, or communal bonfires when they're not out fighting.

I'm pretty sure I've read somewhere of Tyranids spawning bugs with fat reserves and sometimes fur if its super cold. I love the idea of a chubby termagant, so I'm hoping this isn't something I've made up.

 Afrodactyl wrote:
Orks tend to just tough it out, maybe relying on squig pelts to act as windbreaker, or communal bonfires when they're not out fighting.

I'm pretty sure I've read somewhere of Tyranids spawning bugs with fat reserves and sometimes fur if its super cold. I love the idea of a chubby termagant, so I'm hoping this isn't something I've made up.

The extra energy reserves comes from Warriors of Ultramar. Tarsis Ultra was a "winter" planet.