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The BL 12 inch Gun Mark XI and Mark XII〔Britain used Roman numerals to denote Marks (models) of ordnance until after World War II. These were the eleventh and twelfth models of BL 12-inch guns.〕 were British breech loading naval guns of 50-calibres length mounted as primary armament on dreadnought battleships from 1910. ==History== In an effort to increase the armour-piercing capability and range of a 12 inch gun, the 50 calibres/600 inches Mk XI's barrel was 5 calibres/60 inches longer than the previous Mk X gun's 45 calibres. As a result, muzzle velocity increased from to , but bore erosion, which led to short barrel life, and poor accuracy due to inconsistent cordite propellant burning, hampered the gun. The Mk XII derived from it suffered from the same problems. Instead of attempting to improve their 12-inch gun, the British developed the 13.5-inch Mk V gun of 45-calibres, which could achieve greater range at lower muzzle velocities due to its larger shell. Mk XI guns were mounted on: * ''St. Vincent''-class battleships laid down 1907, commissioned 1910 * HMS ''Neptune'' laid down 1909, commissioned 1911 Mk XII guns were mounted on: * ''Colossus''-class battleships laid down 1909, commissioned 1911 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「BL 12 inch Mk XI – XII naval gun」の詳細全文を読む スポンサード リンク
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