The Breech Loading 5.5 inch Mk I was a naval gun used by the British Royal Navy during both World Wars.
This weapon was developed by Coventry Ordnance Works in 1913 and offered to the Greek Navy as main armament for two new cruisers building at Cammell Laird. On the outbreak Of World War I the two ships were purchased by Britain as HMS Chester and HMS Birkenhead. The RN was happy with the performance of the gun as it was significantly lighter than the standard 6 inch gun and fired an 82 lb shell rather than the 100 lb shell of the 6 inch weapon. It therefore had a higher rate of fire with little loss in hitting power. The British ordered more guns as secondary armament for HMS Furious and HMS Hood. A total of 81 guns were made and were used on the following ships
Guns removed from Chester, Birkenhead and Furious were used to arm Armed Merchant Cruisers
 Coast defence gun
In 1940, the 5.5 inch guns were removed from HMS Hood in a refit. Two were installed in Hood Battery on Ascension Island and remain there today. A pair were installed in specially built casemates on the roof of Coalhouse Fort in Essex, overlooking the Thames. Guns from the Hood also went to Bognor Regis, Pevensey, North Foreland, Dover and Folkestone.
 Notable actions
Boy Seaman First Class Jack Cornwell was posthumously awarded the Victoria Cross for heroism in serving his gun on HMS Chester during the Battle of Jutland on 31 May 1916.
 Surviving examples
 See also
 External links