Moncrieff promoted his system as an inexpensive and quickly constructed alternative to a more traditional gun emplacement. The usefulness of such a system had been noted earlier, and experimental designs with raisable platforms or eccentric wheels, with built-in counterweights, were built or proposed. Some used paired guns, in which one cannon acted as the other's counterweight, or counterpoise. An unsuccessful attempt at a disappearing carriage was King's Depression Carriage, designed by William Rice King of the United States Army Corps of Engineers in the late 1860s. This used a counterweight to allow a 15-inch (381 mm) Rodman gun to be moved up and down a swiveling ramp, so the weapon could be reloaded, elevated, and traversed behind cover. The carriage was subjected to six trials in 1869–1873. It was not adopted; an 1881 letter to the Chief of Engineers by Lt. Col. Quincy A. Gillmore stated that it "still leaves a great deal of heavy work to the slow and uncertain process of manual labor". Part of a test installation at Fort Foote, Maryland remains. King's design was better suited for breech-loaders; had the US not had a plethora of new muzzle-loaders just after the Civil War it may have seen wider use. Buffington and Crozier further refined the concept in the late 1880s by allowing the counterweight fulcrum to slide, giving the gun a more elliptical recoil path. The Buffington–Crozier Disappearing Carriage (1893) represented the zenith of disappearing gun carriages, and guns of up to 16-inch size were eventually mounted on such carriages. Disappearing guns were highly popular for a while in the British Empire, the United States and other countries. In the United States, they were the primary armament of the Endicott- and Taft-era fortifications, constructed 1898–1917. Simpler carriages with a limited disappearing function were initially provided for smaller weapons, the balanced pillar for the 5-inch gun M1897 and the Driggs-Seabury masking parapet for the manufacturer's 3-inch gun M1898. However, these could only be retracted at a specific traverse angle (90° off the emplacement's axis), thus could not be used in action. Due to the mount's undesired flexibility when fired interfering with aiming, both types were disabled beginning in 1913 in the "up" position, with installations circa 1903 and later having received pedestal mounts. Both carriage types and their associated guns were removed from service in the 1920s; in the 3-inch gun's case a tendency for the piston