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 the main armament for two new cruisers building at Cammell Laird.

A pair were installed in specially built casemates on the roof of Coalhouse Fort in Essex, overlooking the Thames.

[4] Guns from the Hood also went to Bognor Regis, Pevensey, North Foreland, Dover and Folkestone.

[5] 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.