The Dutchman can be knocked unconscious, held in a choke hold but can't be killed and can disappear at will.
This episode takes place in the 1980s.
During the sequence where Crane and Sharkey are attempting to retrieve the cable, they are using the Flying Sub's rarely seen retractable manipulator arms.
If you look closely, you'll notice that the as rarely seen Flying Sub landing gear is also deployed.
(Presumably to give the arms clearance to operate when Crane rests the FS-1 on the ocean floor.)