The BL 16-inch Mark I was a British naval gun introduced in the 1920s and used on the two Nelson-class battleships. A breech-loading gun, the barrel was 45 calibres long ("/45" in shorthand) meaning 45 times the 16 in bore – 60 ft long.

Description

These wire-wound built-up guns had originally been planned for the cancelled G3-class battlecruiser design upon which the Nelson class drew. Sir W. G. Armstrong Whitworth & Company at Elswick, Vickers at Barrow-in-Furness, William Beardmore & Company at Dalmuir and the Royal Gun Factory at Woolwich made a total of 29 guns of which 18 would be required for both ships at any time. These guns broke with the example offered by the earlier 15-inch Mk I gun, which fired a heavy shell at a rather low muzzle velocity, and instead fired a rather light shell at a high muzzle velocity; this was not a success, as at the initial muzzle velocity the gun wore down rapidly and the accuracy was unsatisfactory, so much that it was lowered. Furthermore, a heavier shell was proposed but not adopted because of stringent budget policies of the 1930s; therefore, this naval gun wasn't seen as particularly successful. An improved weapon, the BL 16-inch Mark II was designed for the Lion-class battleship which was a successor to the King George V class taking advantage of the larger weapon allowed under the London Naval Treaty from March 1938. This "new design" of 16-inch gun fired a shell that weighed 2375 lb. Construction of first two Lion-class battleships - each of which was to have nine 16-inch guns - was halted at the start of the Second World War; only a few months after they were laid down. Work on the armament continued for a while but that was also stopped after only four guns and no turrets were produced.

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