Battle of Kvariam Alpha
As the Tau encroach ever-further into Imperial space, they begin to make a move on the Ocean World of Kvariam Alpha, mining its waters. For a decade Tau operations on Kvariam Alpha go unseen by the Imperium, until it is discovered that they have taken the Ocean World and established deep underwater mining cities throughout its seabed. With the Imperial Guard unable to engage the Tau forces deep below the sea, the Space Wolves are called in.
Gunnar Red Moon's Great Company land on Kvariam's tiny land mass and take the fight to the Fire Warriors that occupy it. The Space Wolves fight off the Tau and establish a beachhead, launching an underwater assault with Land Raiders. They drive deep into the ocean along the sea bed, the advanced airtight Land Raiders and their adamantium hulls immune against the effects and pressure of the ocean. As the Space Wolves vehicles approach the Tau's underwater cities, they disgorge Terminators and are met by propeller-tailed Battlesuits as well as sleek torpedo-armed underwater craft. A desperate, silent undersea battle erupts that eventually sees the Space Wolves victorious when Gunnar shatters the domes of the Tau mining cities.