[js2]

The Jason ROV has a 6-mile tether, so it's possible:

https://en.wikipedia.org/wiki/Jason_(ROV)

Titanic was also discovered with a tethered sled, the Argo:

https://en.wikipedia.org/wiki/Argo_(ROV)

It was then explored with a combination DSV and tethered ROV:

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

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