The 120-pounder Whitworth naval gun was designed by Joseph Whitworth during the 1860s.
It was a rifled muzzle loader and used his hexagonal rifled bore design, the principle of which is described in the article on the 70-pounder Whitworth naval gun.
A number of 120-pounders were bought by the Imperial Brazilian Navy and used to arm some of its ironclads during the Paraguayan War in the late 1860s.
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