The depth charge comment was a reference to how slow the projectiles fired by the turrets are. They explode behind their intended target. The only damage they do is usually to the craft following the intended target.
Projectiles moving faster relative to the enemy ships or perhaps beam weapons of a different color than the enemy's? Or are these researchable upgrades eventually? Missile speed, beam weapon, fire rate, DPS, lots to research.
BTW, mine ran at <2 fps once a decent base got going and the enemies were not being destroyed.