Anime: Tokusou Kihei Dorvack

In the year 1999, the Earth is invaded by a gigantic colony-spaceship. The ship belongs to the Idelians, who have been wandering through space for over ten thousand years. Now, with their vessel almost out of energy, their final hope is to settle in our solar system. The Earth Defense Forces initiate a repulsion effort against the Idelians' sudden invasion in the Alps, but cannot stand against the enemy's powered armour. However, among the Defense Forces is a single unit that proves a match [for the invaders], though their battles are harsh. The team, under the command of Colonel Takashiro Yooichi, is a special unit comprised of three men and three robots, and centered around its human members: Mugen Makoto, Pierre Bonaparte and Louie Oberon. These three men board and do battle in their variable mecha: a jeep, tank, and helicopter, respectively, [machines] conceived for all-terrain combat which transform into robots.

Source: http://1500bc.com/pretf/dorvack.html