“When beholding the tranquil beauty and brilliancy of the ocean’s skin, one forgets the tiger heart that pants beneath it; and would not willingly remember that this velvet paw but conceals a remorseless fang.”
— Herman Melville, “Moby Dick”, Datalinks
In the game, Pressure Domes allow bases to exist underwater. Quite naturally, they are thus unlocked by Doctrine: Flexibility, the same technology that enables ship construction. They also serve as Recycling Tanks, but they don’t stack. So if the base already has Recycling Tanks, there is no economic benefit from having a Pressure Dome, too.
Bases that are built in the ocean with colony pods mounted on a seaborne chassis get Pressure Domes as part of the construction price of the colony pod. This doesn’t count as constructing the dome, so the player almost never hears this quote during gameplay. There are only two real exceptions.
First, the game includes a very robust futuristic terraforming system. With the appropriate technology and the expenditure of energy credits and former turns, it is possible to raise and lower land in the faction’s own territory. Usually a player would use this to raise up mountains to put solar collectors on them and arrange for rain shadows that lead to plots rich in nutrients for him and much less for his opponents to the east. Alternatively, the ground can be flattened to allow for thermal boreholes to be drilled deep into the ground to yield a large amount of minerals and energy.
But, if a player were so inclined, he could also use this feature to submerge one of his own bases. If this were done without building a Pressure Dome in the base, it would be removed from the map when the water overtook the base. So reinforcing the dome there would make sense.
Second, the global sea levels can also rise and fall. There is a trend toward the seas rising as industrial activity leads to global warming, which melts the off-map ice caps of Planet. Additionally, this can be controlled by large-scale geoengineering projects that can be voted on by the U.N. Council later in the game. This makes possible a hilariously evil tactic by which the sea levels are intentionally raised a great deal, drowning everyone’s coastal settlements except for the player’s, since the AI basically never builds Pressure Domes.
With all of that context, Reynolds’s choice of this quote from Melville’s best known work becomes comprehensible. The ocean is scary, just as it always has been. Especially if you contemplate what it would take to live beneath the waves, instead of merely skimming along the surface to harvest the sea’s bounty.
And what lurks beneath the ocean’s skin on Planet is even more terrifying than any whale, shark, or squid found on Earth. For there exists a type of mind worm boil – called an Isle of the Deep – that races above and through the oceans. It can burrow through a reinforced, underwater Pressure Dome just as easily as its above-ground cousins can pierce a standard one.