Sentry Gun
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Basic Information

A sentry gun is a type of robot consisting of a powered turret, some form of firearm or similar ranged weapon, appropriate sensors and a control unit.

The fully automated sentry gun is currently theoretical (but entirely practicable) technology - its deployment hampered more by political than technical considerations, and it appears in a great deal of sci-fi and speculative fiction set from twenty minutes into the future onwards. They are normally deployed to replace human sentries (hence the name), providing armed security for a fixed area. Where the gun's AI is capable of telling friend from foe, the gun can be installed to protect an occupied area, otherwise they are normally left to protect areas where no-one has any business being and switched off when their zone of control has to be entered. The closest living relative known to exist is the Samsung SGR-A1, examples of which can be found covering the demilitarised zone between North Korea and South Korea … there is some dispute as to exactly how autonomous these systems are but officially at least they require the input of a human operator before they can open fire. There is a distinction between man-in-the-loop control (MITL) where a operator's input is necessary to fire, man-on-the-loop (MOTL) where the weapon can fire on its own but has an operator with oversight who can veto any firing, and fully autonomous operation. Which form of control the Koreans are actually using is not public knowledge…

The exact nature of the gun, turret and sensors will vary depending on who has installed them, where and when - a portable unit deployed for flank protection by an infantry platoon is probably far less impressive than an automated turret designed to protect a key mountain pass from enormous mecha. Likewise, the more permanent and expensive the mounting and its supporting sensors, the more accurate it can be expected to be - but in general expect them to be far more accurate than a realistic human marksman … a sentry gun is never shaky, rushed, tired or anything else that interferes with a human's shooting. Turrets may be occulted and/or armoured in the right context and will vary greatly in their supplies of power and ammunition. Some designs may be built to make a verbal challenge to potential targets and/or issue a warning … others may not.

Telling a fully automated sentry gun from a remote controlled gun turret might well be tricky - indeed, many designs may permit operator control or require human permission to open fire, depending on who has installed them and where.

Despite the robot bit, magitek versions based on golemcraft could probably be inserted into a fantasy campaign as well. The "magic statue that shoots bolts of fire" is probably the most direct expy.


1. full source reference

Game and Story Use

  • Where these things exist, hacking them is probably a standard part of military and intelligence training.
    • The lateral thinker can also interfere with their power supply, cut off their ammunition feed, blind their sensors or just shoot them. Portable versions may even be easily silenced by knocking them over.
    • Research, or appropriate knowledge skills might also identify likely no-fire zones or other useful information ("If you can get right next to a Mk12B, it will assume that it is being serviced and go into safe mode").
  • As all Deus Ex players know, much fun and laughter can be had by reversing the IFF protocols on one of these.
  • GMs can also annoy PCs by playing with the parameters of the gun's AI: so what if the horde of alien locusts is overunning your base? The guns aren't shooting at them because they were re-programmed to stop them shooting at the local wildlife all the time, and the alien locusts look just like the local wildlife to the gun's sensors…
  • Something no-one wants to hear as they emerge into the daylight from the sewers of death/escape tunnel/deadly underground labyrinth: "Warning! Automated Defence System Active! This system will open fire in 10 … 9 … ".
  • Likewise, "Activating the perimeter defences" can be a useful mini-goal for PCs in the right sort of adventure.
  • These are good general adversaries for most modern and sci-fi games - plus even the most literal pacifist can usually get into shooting them.
  • Gadgeteers may be able to salvage useful weapons and parts from a demolished sentry gun.
  • Having a lot of sentry guns kicking about gives a somewhat dystopian air to the setting.
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