Does any faction in the world of Warhammer 40K take prisoners of war?

Question

This may be a completely naïve question, but as I understand Warhammer 40k has been inspired by the Roman empire and the Second World War. The Roman empire generally enslaved or killed prisoners that were captured after battles, while (almost) every side in the Second World War captured prisoners and kept these persons either in a PoW camp or put them to work. With these facts in mind, does any faction in the world of Warhammer 40k keep prisoners of war that are captured on the battlefield?

I can imagine that chaos troops are executed after battles rather than being kept due to the risk of turning other Imperial troops to chaos, if that is possible?

Answer 1

Imperium

The Imperium of Man is, as the name states, for humans and humans only. Xenos are not tolerated and certainly not accepted within its borders. So, they wont take any PoW from Xenos, they'll even eradicate the civilians from planets they conquer.

Chaos is the arch enemy, even worse than Xenos. While temporary alliances with Xenos, e.g. Eldar, can be tolerated, Chaos is eradicated when sighted. However, simply cause a planet was invaded by Chaos does not mean that all are killed. But all are deported and e.g. put into work camps, as can be with the first war for Armageddon:

Although they had won, the victorious soldiers of Armageddon were doomed. They had gained knowledge of the existence of Chaos, and been exposed to its corruption. The Inquisition had all of the people who fought on the planet, except for the Space Marines, sterilized and placed in work camps.

From the Lexicanum article on the First War for Armageddon

If a planet with a human population is conquered, they are not simply eradicated. The planet then belongs to the Imperium and has to pay its tithe. I can imagine, but have no quote, that human soldiers are integrated into the Imperial Army (probably as Penal Legion).

Chaos

Forces of Chaos raid planets in order to get slaves for their dark purposes like the Daemonculaba. They do not only take humans as slaves but also e.g. geneseed of other loyalist Space Marine chapters. So, they take PoW directly and some CSM could be considered PoW as they're not in the chapter they'd belong to.

Eldar

Eldar don't fight traditional wars like humans do, they also consider humans and other races as inferior. They kill or evict people from planets they consider theirs.

Dark Eldar

Dark Eldar also don't wage war like humans do, they raid with the specific purpose of getting slaves they can put to work or torture. So, in a way, they take PoW but death would certainly be the more merciful way.

Orks

Orks also don't wage war, they fight. While humans consider it a war (e.g. Second War for Armageddon), for Orks, it's simply leisure time. I don't think they take PoW, that would be a waste of enemies they can fight (but have no quote)

Tyranids

They eat everything they meet, so you win or get eaten.

T'au

T'au make use of human soldiers, they are combined in the Gue'vesa Auxiliaries:

The Gue'vesa (literally, "Human Helpers") are Human soldiers who serve as Auxiliaries in the Tau military.

From the Lexicanum article on the Gue'vesa Auxiliaries

Also, when they've conquered a (human) planet, those that are against the new rulers are not killed but reeducated or sterilised:

Whilst many assimilated humans do enjoy more liberties and comforts than they did under Imperium rule, those who stubbornly resist are sometimes interred in re-education camps or subjected to sterilisation programs.

From the Wikipedia Article on the T'au Empire

I imagine that human soldiers that see the error in their way are included into the Gue'vesa Auxiliaries and those that resist are sterilised.

Necrons

Not a unified force. There are some like Trazyn that don't simply kill everything but, in his case, collect some and put them into stasis in his collection (which can be considered PoW)

Answer 2

The 40K novel Death or Glory has Ciaphas Cain rescuing (unwillingly) slaves from Orks in the town of Prosperity Wells.

The Dark Eldar are identified as slavers (one can argue the point, but I don't think you get particularly far).

The Inquisition of the Imperium captures Xenos for experimentation (First example that pops into my head is Warhammer 40,000: Space Marine but there is at least one example in one of the Ciaphas Cain books)

There are quite a few other examples across the novels of characters being taken hostage, imprisoned, interrogated, etc., but these are one offs and I don't entirely believe they cover the question as asked.

More generally, just like the fluff is designed such that every fraction has a reasonable reason to fight every other faction (and themselves) you end up with being able to justify POW by almost every race except possibly the Tyranids (and I would argue that humanoids implanted by Genestealers count as capture in a sense)

Answer 3

Shade's answer is the correct answer however if you're willing to go back to the 30th Millenium there are a few examples in The Great Crusade and Horus Heresy.

During the Great Crusade if an expeditionary fleet encountered a world which needed to be forced into compliance then they would subdue the planet. This is more akin to an invasion, however it's safe to assume that some figureheads were imprisoned or converted into servators rather than all being killed.

We also know that there are prison facilities in the Terran System. Garro was a "guest" at one of these along with the 70. They were loyalists from the 14th Legion and were held on Luna until their loyalty could be determined.