SWIV

SWIV is a vertically scrolling shoot-em-up which plays in a typical fashion to other games in its genre. The player chooses between using either a helicopter or a jeep at the beginning of the game and then plays in their chosen vehicles through scrolling levels, shooting at oncoming enemies. If two players are present, both vehicles will be used at once. Certain enemies when shot drop shield power-ups which can be either picked up to afford temporarily invincibility or detonated to destroy all enemies onscreen. Every so often a boss enemy will attack. The destruction of these bosses will give upgrades to the player's forward firing gun.

Source: Wikipedia, "SWIV", available under the CC-BY-SA License.