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Are Space Marines (no matter the chapter) capable of fighting in a underwater environment?

Any book or game is welcome as a source but not fanfiction.

  • I'm at a loss how this is "too broad". Hmm. I've tightened up the question to ask whether they're capable rather than asking for a list of instances. – Valorum Oct 1 '16 at 14:09
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In the Horus Heresy book "Fulgrim", we see underwater fights involving the Space Marines (Astartes / Emperor's Children) on the watery world of Laeran.

There are multiple undersea engagements.

The war for Laeran was fought across many varied battlefields, the warriors of the Emperor’s Children fighting on floating atolls and through the ruins of ancient structures that reared from the oceans, while foaming breakers crashed against walls that had once stood thousands of metres in the air.

Underwater cites were discovered within days of the campaign’s opening and detachments of Astartes took the fight to the abyssal darkness of undersea trenches, smashing into structures that had never known the touch of sunlight, in specially modified boarding torpedoes fired from cruisers hovering above the sea.

According to Codex: Space Wolves, Space Marines are capable of breathing water

Regardless of his Chapter, each Space Marine has a secondary heart and an auxiliary multi-lung, allowing him to survive massive damage to the torso and fight on regardless. He can sustain and swiftly recover from wounds that would cripple or kill a mortal man, hibernate for decades, breathe water or poison with no ill effects, spit acid at his foes and even absorb an enemy’s memories and thoughts by eating and assimilating their flesh. Space Marines are the creations of the Emperor himself, and they share a measure of his power.

And gives another example of a deep-sea battle, this time involving the Space Wolves Legion. Evidently the Imperial Guard weren't up to the task, so they needed a Space Marine legion to do the job.

The Tau Empire, encroaching ever further into Imperial space, mines the bed of the ocean world of Kvariam Alpha. It takes a full decade for the domes and corridors that stretch along the ocean floor to be discovered by an augur probe. With the Imperial Guard unable to engage the Tau forces so far below the sea, the Space Wolves are called in.

...

As the tanks near the alien domes and spires of the Tau cities to disgorge their Terminator-armoured passengers, circular portals in each section fan open and teams of graceful, propeller-tailed battlesuits move to intercept the slowly approaching armoured column. A desperate, silent undersea battle erupts, but despite the bewildering array of sleek torpedo-armed craft brought to war against them the Space Wolves still manage to shatter the domes of the Tau mining operations. The sea around them is choked with corpses before the Tau finally flee.

  • Lovely, just lovely, thanks @valorum, again for responding to my question. Crystal clear! It amuses me though, thinking about bulky space marines swimming into battle – Schneejäger Oct 1 '16 at 23:20
  • It's been canon all the way back to the original Rogue Trader book if anyone cares. I don't have my copy anymore (hence moment not answer) but I do recall them talking about marines and their powered armor and specifically talking about being able to handle vacuum, deep sea, even harsher climates like planets with corrosive atmosphere and such. – Paul Oct 2 '16 at 13:18
  • I read about their armour and implants that handle easily extreme conditions and take punishment that could destroy tanks (that's a direct quote from DoW2 I believe). – Schneejäger Oct 2 '16 at 17:35
  • I've got a funny feeling something is mentioned when Horus' is being tempted in the 2nd Horus Heresy book and 'Sejanus' is floating down the river. I think it might even state that they can't drown – TommyBs Oct 2 '16 at 20:03

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