Gowapper 5 Gordam
English name: Goliath the Super Fighter
Genres: Action, Adventure, Sci-Fi
Type: TV, Episodes: 36
Aired: Apr 4, 1976 to Dec 29, 1976
Studio: Tatsunoko Production
Source: Original
Rating: PG-13 - Teens 13 or older
Synopsis:
Five youths from Edo City explore a strange rocky island and discover the mecha that Doctor Hoarai had been creating in order to resist the impending attack by a race of subterranean rock people. 

Doctor Hoarai was ridiculed by the scientific community for his predictions that such an attack would take place. The youths decide to join the doctor (who was dead but had transferred his mind into a computer) in piloting the vehicles and protecting Earth. The Gowapper 5 Gordam team is born! With the aid of the giant fighting robot Gordam, the Gowapper team under the leadership of Youko Misaki must face the hordes of the inhuman subterranean people.

(Source: AniDB)