H0347825 (hī′drō-nôt′)n. One trained to pilot, navigate, or otherwise participate as a crew member of a deep-sea vessel.
hydronaut
(ˈhaɪdrəʊˌnɔːt) n (Military) navyUS a person trained to operate deep submergence vessels[C20: from Greek, from hydro- + -naut, as in aeronaut, astronaut]