 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.