Sentry Gun (Red Alert 2)

The Sentry Gun was an automated Soviet defense mechanism that was introduced during Great World War III. It was a robotic gun turret that used a rudimentary AI to fire on enemy soldies and leave friendly ones unharmed. It was built as a Russian equivelent to the Allied.

Great World War III
Despite the Soviet Union being known for its nay-obsessive propensity for excess firepower, the removal of the ridiculously deadly flame tower from their World War II arsenal at the dawn of Great World War III stands as proof that the battle crazed nation had some ability to limit itself. Realizing through the greivous trials of the second world war that the flame-thrower mounted watchtowers of the past were as dangerous to Soviet troops as they were to Allied ones, the Red Army quickly sought out a suitable base defense to act as a safer replacement. Utilizing AI technology, Soviet military scientists developed the sentry gun, an automated gun turret that fired 12.7 millimeter bullets at a blindingly rapid clip. Using a simple camera "eye" and early "friend/foe" programming, the turrets were able to detect who was a member of the Red Army and who was not via visual approximation, essentially telling the machine who to shoot and who to avoid shooting at. While designed mainly for killing infantry, something which they excelled at, the sentry gun's were also fairly effective against lightly armored vehicles and even did reasonable damage to their heavilly armored brethren. In suitable numbers, the turrets could combat most basic threats.

Sentry guns had two major weaknesses. First off, they were only able to swivel left and right on a simple wheel joint, making it impossible for them to shoot down aerial targets. Second, because the turrets relied on visual accuity to determine enemies, they were unable to fire upon disguised spies.

Great World War III (Second Iteration)
The Sentry Gun was seen again after (or if you want to be chronologically accurate, before) the Psychic Dominator Disaster, being basically identcal to their pre-Disaster counterparts. The only difference came with their programming; the new Sentry's were re-programmed to attack Yuri soldiers in addition to Allied ones, with the Allied attack programming being dropped at the end of the war with the East/West alliance.