hydronaut

hy·dro·naut

 (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) navy US a person trained to operate deep submergence vessels
[C20: from Greek, from hydro- + -naut, as in aeronaut, astronaut]
References in periodicals archive ?
A new LEGO(r) SYSTEM play theme -- Adventurers -- makes its debut, along with several new mini-themes, including: Insectoids, Ninja, Hydronauts, Stingrays, Extreme Team and ResQ.