It seems that the wires prevent the drones to go further inside the ship, so I wonder if they can be made wireless? If radio is not working in such conditions maybe sonic or light signal can get through?
Nowadays, we could probably build it smaller, untethered, and semi-autonomous (but that hunch is not intended to undercut the tons of work it would take to do it).
It's entirely possible data couldn't be delivered back to the parent machine until a physical connection could be established; not sure if acoustic signalling can be made high-bandwidth enough for video. Line-of-sight laser modulation could be used for high-bandwidth once the ROV is out of the bulk of the ship.
Visible light is pretty much just the portion of the EM spectrum that is poorly absorbed by water [0] (and that is also produced by the sun and also poorly absorbed by atmosphere)
If radio worked well in water (where eyes first evolved), then we would just "see" radio waves (except in practice the Sun doesn't make enough of them that reach Earth).
[0] http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.h...