embark in the ocean/caves. For some reason, it doesn't reveal caves and teleports dwarves in the rock, where they get crushed in the first ticks. Gruesome deaths, instant settlement withering. So I did the following:
* deep-embark --depth CAVERN_1
* gui/gm-editor df.global
* pause_state true
* reveal
* First the cavern closest to the surface.
* Find its coordinates, then teleport the dwarves there, as well as the animals (I thought the animals would be crashed in rock for some reason, so I only accidentally took two yaks; accidentally because I didn't want to take them at all).
** In case this isn't clear, animals can be teleported as easily as dwarves, so if ever building under the ocean, use those points for animals!
* Create pickaxe and actual axe via
createitem because all the tools on embark are lost; if they can be teleported, I don't know how to, and at this point I don't know where they are or if they are destroyed like tools are destroyed in obsidian.
* Mine a part of the caves close to the miner.
(The game so far should not be unpaused)
* Unpause until the miner equips the pick and the wall to be mined starts blinking.
* Pause and then unreveal.
* When the first wall is mined, the caves are "discovered".
* Play as usual.
Noticed issues:
* Farming is a MUST. Cave plants have run out really fast.
* It's like playing a micro-fort. The caves are compressed together that there's relatively little height to play with.
* Caravans and even the second dwarf wave don't arrive while the map is flooded. Who'd have guessed? I was stuck with 7 dwarves that I planned to take some from Blueocean, but then I realized how far and treacherous it would be through the caves, so I just let it exist there.
* Another note is what I've done some other time in a frozen ocean biome, you can make a 5x5 obsidian pillar via DFhack to get to the surface; I didn't, because it'd be flooded on reclaim.
* Water is relatively easy to find, I found some in the first layer.
* One issue is that it's not really rich. It doesn't even have
granite. Well, there's some granite below magma, but that's really hard to get to. Thankfully, it
does have above-magma marble.
* There's an interesting thing on cave generation where they actually end before the western and northern map ends, so that's cool.