A significant number of broadside ironclads were built in the 1860s, principally in Britain and France, but in smaller numbers by other powers including Italy, Austria, Russia and the United States. The advantages of mounting guns on both broadsides was that the ship could engage more than one adversary at a time, and the rigging did not impede the field of fire. Broadside armament also had disadvantages, which became more serious as ironclad technology developed. Heavier guns to penetrate ever-thicker armor meant that fewer guns could be carried. Furthermore, the adoption of ramming as an important tactic meant the need for ahead and all-round fire. These problems led to broadside designs being superseded by designs that gave greater all-round fire, which included central-battery, turret, and barbette designs. Turrets, batteries, and barbettes There were two main design alternatives to the broadside. In one design, the guns were placed in an armored casemate amidships: this arrangement was called the 'box-battery' or 'centre-battery'. In the other, the guns could be placed on a rotating platform to give them a broad field of fire; when fully armored, this arrangement was called a turret and when partially armored or unarmored, a barbette. The centre-battery was the simpler and, during the 1860s and 1870s, the more popular method. Concentrating guns amidships meant the ship could be shorter and handier than a broadside type. The first full-scale centre-battery ship was of 1865; the French laid down centre-battery ironclads in 1865 which were not completed until 1870. Centre-battery ships often, but not always, had a recessed freeboard enabling some of their guns to fire directly ahead. The turret was first used in naval combat on in 1862, with a type of turret designed by the Swedish engineer John Ericsson. A competing turret design was proposed by the British inventor Cowper Coles with a prototype of this installed on in 1861 for testing and evaluation purposes. Ericsson's turret turned on a central spindle, and Coles's turned on a ring of bearings. Turrets offered the maximum arc of fire from the guns, but there were significant problems with their use in the 1860s. The fire arc of a turret would be considerably limited by masts and rigging, so they were unsuited to use on the earlier ocean-going ironclads. The second problem was that turrets were extremely heavy. Ericsson was able to offer the heaviest possible turret (guns and armor protection)