Tail Gunner is a monochrome vector arcade game. The premise of the game is that the player is the tail gunner of a large space ship. It is a first-person 3-D game as the monitor represents a gunner's view port.
As successively faster formations of 3-D enemy spacecraft approach, the player must aim a set of cross-hairs and shoot the enemies before they can fly off the screen and slip past the player's ship. In addition to shooting down the enemy ships, the player is also given limited use of a shield that can block ships from passing. Ships hitting the shield bounce back and if the player is quick these can be shot before they disappear from view. The game ends when ten ships have slipped past the player.
Source: Wikipedia, "Tail Gunner", available under the CC-BY-SA License.