Gowapper 5 Gordam

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)