The Viking, a very versatile unit in the Terran armada, can be used for both ground-to-ground and air-to-air combat. While certainly a great unit on its own merit, it should not be the only component of a budding Terran commander’s army, requiring proper support when not raiding the enemy mineral line or hunting overlords.
The Viking can be built straight from the Starport and receives the innate ability to switch between air and ground mode.