The Hazardous Environment Combat Unit Sentry Gun, commonly referred to as the HECU Sentry Gun, is a fully autonomous weapon. Sentry Guns are commonly used by the HECU, the Black Ops and eventually the Allies and Axis, to guard areas of strategic value. However, the Combine have their own varity of sentry gun known simply as the Combine Sentry Gun, to guard areas of strategic value
The sentry gun consists of a powerful machine gun built onto a tripod, mounted on a turntable unit allowing it a 360 degree field of view. Unlike its successor, which has a limited field of view.
Some of these guns relied upon an independent laser sensor to detect targets while others were deployed, without one.
Once an enemy has tripped the beam, was detected automatically, by contact, firing close or simply damaging it then it activates, accompanied with a high pitched whine, and shoots at the sighted target.
Once alerted, the sentry would remain that way for a short time, and made a steady beeping sound as it scanned for targets while, before sinking back into its docile, standby, mode.
Despite its comical appearence, these guns were in fact rather resilient to gunfire and are difficult to knock over but any sufficient type of damage will knock them over, with explosives being the most effective tactic.
Orginally developed by the United States Military on Golmar in the early 1330s. The sentry gun deployed to either special operations units (like HECU) or Black Operations units (like Black Ops). However, following the Seven Hours War and the substantial occupation that followed, these turrets were placed in hidden military bases across the former United States where it was then discovered by the Earth Freedom Fighters who then modify them for their uses, which eventually lead to their use throughout the Alliance of Nations in 1415 when the Human-Vortiguant Federation introduced them to it's new found allies. Unfortunately, a shipment of sentry guns were captured by the Axis which then reverse engineered them and proceeded to produce their own variety of sentry guns