A larger structure serving the same purpose as a
turret, compared to the stand-alone gun,
turret.
Commonly used outside the US where proper
English DOES exist. It should be added to an English dictionary, if it has not been already.
Turret is instead used as being part of a tower or building.
It might also relate to a more automatic and continuously firing weapon.
Regardless of the differences, it is sometimes used interchangeably with
turret and found in both forms in video games.
The missile turrent was a base defence while the naval boats had turrets as their means of combat.