John Hart (The Sea Devils)

You may be looking for John Hart (Kiss Kiss, Bang Bang) Captain John Hart of the Royal Navy worked at a secret naval research centre. Jane Blythe worked as his secretary.

Biography
The Third Doctor arrived at the base and Hart telephoned security when he saw him beach. He was brought to Hart where he explained he was from UNIT. After Jo Grant was able to clarify this he let them go.

Hart refused to have the Doctor taken to a sea fort station, describing it as "joyriding him around". After the Doctor and Jo were reported missing he telephoned for an air sea rescue helicopter.

He was captain of the HMS Seaspite; the ship was converted into a SONAR testing station. (DW: The Sea Devils)