Do you know what Hydronaut’s question was? This aquatic sci-fi film from a time when they were all the rage, Andrew Marton’s effort isn’t terrible, but it just moves along without ever becoming truly thrilling. The cast includes Lloyd Bridges, Brian Kelly, Shirley Eaton, David McCallum and Keenan Wynn, who are responsible for traveling across the ocean floor to place sensors that will alert people about approac…