There are several companies specializing in deep see ROV applications, it's a super interesting field.

https://en.wikipedia.org/wiki/Remotely_operated_underwater_v...

Is a great starting spot, read it and then branch out following the sources links.

I went to sleep, time zones being what they are, but see that user jacquesm posted a link to a most impressive rabbit hole of engineering porn.

As an aside, one of the first field jobs I attended after graduating was commissioning some equipment fitted onto the R/V Knorr, the very ship which was used for finding the Titanic.

For a Titanic buff, that was a great experience - doubly so when the project manager at the Woods Hole end found out that I had more than a passing interest in the wreck, and during lunch one day suggested we go see if we could find Bob, as he believed him to be on the premises.

Bob, of course, turned out to be Robert Ballard, who turned out to be an incredibly gentle and patient guy who answered each and every question I had like it was the first time he had it posed to him, despite probably having had them thousands of times before...

I've done some work for a company in this domain, it is incredibly interesting and you could easily lose several lifetimes on all of the engineering details.