Photo of a <a href="https://en.wikipedia.org/wiki/QF_6_inch_/40_naval_gun" class="extiw" title="en:QF 6 inch /40 naval gun">QF 6 inch Mk III naval gun</a> from HMS Calypso. 
<p>On display at <a href="https://en.wikipedia.org/wiki/Fort_Nelson,_Hampshire" class="extiw" title="en:Fort Nelson, Hampshire">Fort Nelson, Portsmouth</a>. It was built in 1893 and was built by the Elswick Ordnance Company.
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For rear view see <a href="//commons.wikimedia.org/wiki/File:6_inch_gun_from_HMS_Calypso_rear.JPG" title="File:6 inch gun from HMS Calypso rear.JPG">File:6 inch gun from HMS Calypso rear.JPG</a>.
geni
CC BY-SA 4.0
Photo by <a href="//commons.wikimedia.org/wiki/User:Geni" title="User:Geni">user:geni</a>