[fghorow]

"Undersea mining" is mostly scooping up mineralized stuff ("Manganese Nodules") using a dredge-like apparatus. To my knowledge, nobody uses explosives for that style of mining, and undersea mining is relatively rare anyway. (I used to work at the research end of the Australian mining industry.)

[dosman33]

I was under the strong impression that sea floor mining was mostly invented as cover by the CIA to operate the Glomar Explorer for the purpose of retrieving a crashed Soviet submarine with nuclear warheads on board. https://en.wikipedia.org/wiki/Glomar_Explorer

The US petitioned the UN to open up international sea floor mining rights as part of the lead up for this project. They made up a fake educational film for high schoolers about Glomar as well: https://www.youtube.com/watch?v=qXUqUpfzgxQ

[kragen]

I think manganese nodules really are a potentially lucrative source of metals; the CIA didn't want to use a cover story that was transparently ridiculous, and there were many excellent Soviet geologists and mining bureaus.

[snovv_crash]

Diamond mining off the Namibian coast is similar, it's just a giant underwater vacuum cleaner.