Either HMS <i>Implacable</i> or HMS <i>Indefatigable</i> with HMS <i>Anson</i> in the background - 4.5"/45 (11.4 cm but actual bore is 4.45 inch as with all British 4.5 inch ordnance, or 11.3 cm and this latter one is preferred for metric description) Mark III guns in RP10 Mark II BD (below deck) mountings
RN
unknown IWM photo (CPL=?), <a rel="nofollow" class="external free" href="http://www.navweaps.com/Weapons/WNBR_45-45_mk1.htm">http://www.navweaps.com/Weapons/WNBR_45-45_mk1.htm</a>