Diagrams showing Rocking bar sight for British <a href="https://en.wikipedia.org/wiki/Ordnance_QF_18_pounder" class="extiw" title="en:Ordnance QF 18 pounder">QF 18 pounder field gun</a>.
British Government
<p>Plate XI of "Handbook of the 18-PR. Q.F. GUN - Land Service", 1913.<br></p>
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