Pivot gun

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a gun mounted on a pivot or revolving carriage, so as to turn in any direction.

See also: Pivot

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
(4) "C" pivot offers to a Central pivot gun emplacement where the mounting could turn a full 360 degrees.
It was a pivot gun under his command that played a key role in the surrender of Forts Hatteras and Clark at Hatteras Inlet in August 1861.