In Gorlin's design, the helicopter can face and shoot in one of three directions: left, right, and forward ("forward" means facing the screen, useful for attacking ground targets).

The player must use the helicopter to release the hostages, who are trapped in destructible prisons.

Once a prison has been breached, the helicopter must then carefully land and allow the hostages to board, one by one, until the maximum number for a run is reached or it becomes necessary to escape.

The helicopter must then take off, fly back to the base and again carefully land, allowing the freed hostages to leave one by one.

The process then repeats until all hostages from the level are freed or destroyed, preferably not by accident with the player's own helicopter.

Much like the ship in Defender, the player's helicopter in Choplifter is constantly under attack, this time from both ground and air enemies, with high difficulty being the rule, rather than the exception.

Entex's Defender electronic game, which was a popular dedicated handheld from 1982. Entex also released the now highly collectible and rare Adventure Vision tabletop videogame system in 1982, which was bundled with a Defender cartridge.

As with most legendary and popular games, Defender received more than its fair share of additional ports, clones, knock-offs, and enhanced variations.

Some of the best of these include Big Five Software's Defense Command (1982; TRS-80), Sirius Software's Repton (1983; Apple II, Atari 8-bit, Commodore 64), Arena Graphics' Dropzone (1984; Atari 8-bit, Commodore 64, Sega Game Gear, and others), Synapse/Atarisoft's Protector II (1983; Commodore 64, Radio Shack Color Computer, TI-99/4a, and others), and Logotron's Star Ray (1988; Atari ST, Commodore Amiga, and others), which became the officially licensed Revenge of Defender when it was later published by Epyx.

Of course, Defender was also influential for the side-scrolling shooter genre in general, which included Scramble (Konami, 1981; Arcade), where the player had to destroy fuel tanks to replenish their ship's supply while wreaking havoc; Parsec (Texas Instruments, 1982; TI-99/4a), noted for its speech-enhanced audio; Datamost's The Tail of Beta Lyrae (Datamost, 1983; Atari 8-bit); which featured semi-random levels, R-Type (Irem, 1987; Arcade), which became known for its impressive bio-organic graphics and boss battles; Parodius (Konami, 1988; MSX), which parodied the genre and its classic progenitor, Gradius (Konami, 1985; Arcade); and Gates of Zendocon (Epyx, 1989; Atari Lynx), which offered 51 levels to blast through. Despite their popularity, however, unlike Defender, most of those titles relied on more straightforward shooting-based gameplay and an excess of hazards for thrills.

Screenshot from the Commodore 64 version of Revenge of Defender.

The Magnavox Odyssey2's Freedom Fighters! (1982) was that platform's answer to Defender, and, instead of mapping controls to the console's keyboard, implemented an awkward two-joystick control scheme that worked best with two players at the helm. Image from the Freedom Fighters! Manual shown here.

Screenshot from Universal's Cosmic Avenger (1981), a difficult side-scrolling shooter that featured a minimap of limited utility. Defender directly influenced games like this and countless other shooters in a variety of ways.