A barbette was a type of gun mounting popular in late Victorian battleships. It allowed a heavy gun to be carried and the ammunition protected without the weight implications of a full turret. A barbette was essentially an open topped turret, with an armoured shield to protect the gunners and ammunition from side on fire, but with no overhead protection. This meant that only the guns themselves had to rotate, the rest of the equipment could be stationary and this led to a great saving in weight and complexity and in turn made the ship cheaper to construct. This late Victorian postcard depicts one of these barbettes on the quarterdeck of a battleship:

The guns themselves have tompions in the muzzles to prevent rain water entering, but they look to be 12″ guns so this is clearly a capital ship:

Three sailors pose beside the guns, one in the white working uniform and the other two in the standard dark blue wool uniform:

Whilst barbette mounted guns were relatively hard to hit with flat fire at close range, as the range of gunfire increased shells tended to land from above in a long arc and with no overhead protection, barbettes were very vulnerable. One hit would disable the gun, kill the gun crew and might set off a magazine explosion that would destroy the whole ship. By the turn of the twentieth century technology had advanced to such a point that turrets could be build as one piece, with all the ammunition stowage and handling being completed below the turret and the open topped barbette was dropped from naval design, having only seen thirty or forty years service, in favour of the armoured turret we are so familiar with today.