In 1877 the Defence Committee noted that more powerful guns of 80 tons had been developed and they recommended that a turret be fitted on the Admiralty Pier Fort for two 80-ton guns. The Superintendent of the Royal Gun Factory had been asked for designs for a powerful gun for capable of penetrating 20 inches of iron at a range of 1,000 yards and it was these guns that were eventually used as armament for the turret on the Admiralty Pier Fort. The gun took 18 months to build and by September 1875 the first gun was ready. Following test firings at the Royal Arsenal the gun was hauled onto the barge "Magog" and taken to Shoeburyness.