 While a few units used in fixed fortifications were sometimes mounted on sinking platforms or on short rail stubs intended for tactical concealment, the overwhelming majority were not, and acted in action as completely fixed guns, and are outside the subject of this article.Retractable turrets were also conceptually similar, but almost never depended on recoil actuation, and, like the balanced pillar systems, often remained visible when actually in operation.Unlike balanced pillar designs, the pieces could generally be pointed and trained from cover, allowing complete surprise for the first shot.