The first operational use of a rotating turret was on the American ironclad , designed during the American Civil War by John Ericsson. Open barbettes were also used to house their main batteries on rotating mounts. Both designs allowed naval engineers to dramatically reduce the number of guns present in the battery, by giving a handful of guns the ability to concentrate on either side of the ship. In time this trend reversed, with a proliferation of weapons of multiple calibers being arranged somewhat haphazardly about a vessel, many in mounts on the hull or superstructure with limited travel. Confusion also arose when combinations of large caliber "main battery" and smaller "secondary battery" weapons of mixed offensive and defensive use were deployed.