The Tech Turret is a neutral defensive structure that, when captured by an Engineer, is basically a rotatable cannon turret which can effectively engage vehicles.
An anti-armor turret used to destroy vehicles. A cheap, maintainable defense that requires no power.
The Tech Turret is simply a capturable Gun Turret but has more hit points and slightly stronger in firepower. It can engage standard vehicles (including main battle tanks) on its own, but will have difficulty taking down heavier vehicles.
Unfortunately, if the Tech Turret is by itself, enemy Engineers can capture it without fail, as the Tech Turret can do little against infantry, even the most vulnerable ones.