The WST is a small cannon, often seen on Royal Navy MK3 Corvette. It is the cheapest of the SiB turrets in terms of TNT cost per shot. It is a standard design in terms of firing style, using two projectiles that travel the same arc to hit the target. Curiously, several users have reported that early SiB spawned mk3 corvettes had WSTs that could self detonate, crippling the ship.
Contrary to the name, it is not the smallest turret however possibly was at the time of its creation.