to lower the center of mass as to afford protection, and resembled a "lift battery." The gun was not normally lowered between shots. Related and parallel systems U.S. Endicott-era balanced pillar and masking parapet mounts were, in a sense, a hybrid of simple pedestal mounts and disappearing mounts: the guns were hidden from observation while out of action, but, once engaged, remained vulnerable to direct observation and direct fire. The emplacement designs only permitted retraction with the gun barrel at a specific traverse angle, usually 90° off the emplacement's axis. Since the barrels substantially overlapped the parapet of their installation, it was impossible to point the piece while concealed. The balanced pillar mount was used primarily with the 5-inch gun M1897, while the masking parapet mount was a Driggs-Seabury patent used primarily with the manufacturer's 3-inch gun M1898. "Masking parapet" was a proprietary term coined by Driggs-Seabury to distinguish their carriage from balanced pillar designs. Beginning in 1913 these carriages were disabled in the "up" position due to undesired flexibility interfering with aiming. The M1898 3-inch gun also developed a tendency for the piston rod to break when fired, and both types and their associated guns were removed from service in the 1920s. In 1893 Germany's Hermann Gruson developed an armored turret for a 53 mm gun called a "Fahrpanzer" (mobile armor) that had both road- and rail-mobile versions. These were sold to several other countries prior to World War I, notably Switzerland, Romania, and Greece, were widely deployed in that war, and were present in most major Swiss fortifications at least through World War II, including Fort Airolo. Surviving examples of the Fahrpanzer are at the Athens War Museum and the Brussels Army Museum. These mounts were intended for use in prepared trench-type positions that would shelter them from view when retracted; in the Swiss forts they were stored in covered bunkers until repositioned to fire. 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