Different weapons are often suited to different enemies, but these games seldom keep track of ammunition.
As such, players tend to fire indiscriminately, and their weapons only damage legitimate targets.
The genre's origins can be traced back to Spacewar!
, one of the earliest computer games, developed in 1962 and eventually released in amusement arcades in the early 1970s.
Examples include Space Harrier (1985), Captain Skyhawk (1990), Star Wars: Rebel Assault (1993), Panzer Dragoon (1995), Star Fox 64 (1997), and Sin and Punishment (2000).
Light-Gun games that are "on-rails" are not in the shoot-em-up category but the FPS category, Run and gun (or "run 'n' gun") describes a shoot 'em up in which the protagonist fights on foot, perhaps with the ability to jump.
Run and gun games may use side scrolling, vertical scrolling or isometric viewpoints and may feature multidirectional movement. was developed at the Massachusetts Institute of Technology in 1961, for the amusement of the developers; it was, however, remade four times as an arcade game in the early to mid-1970s. The game used alien creatures inspired by The War of the Worlds (by H. Wells) because the developers were unable to render the movement of aircraft; in turn, the aliens replaced human enemies because of moral concerns (regarding the portrayal of killing humans) on the part of Taito Corporation.
As with subsequent shoot 'em ups of the time, the game was set in space as the available technology only permitted a black background.
The game received acclaim for its surreal graphics and setting and the protagonist, Opa-Opa, was for a time considered Sega's mascot.Later in the 1970s, games such as Space Invaders and Asteroids popularized the genre.Shoot 'em ups were popular throughout the 1980s and early 1990s.Vertical scrolling shooters emerged around the same time.Namco's Xevious, released in 1982, is frequently cited as the first vertical scrolling shooter and, although it was in fact preceded by several other games of that type, it is considered one of the most influential.