30"70

This gun was originally a US postwar naval anti-aircraft gun developed in a joint project with the United Kingdom. Designed by Vickers for British aircraft carriers and Tiger-class cruisers beginning in 1956 and later used on Canadian Restigouche and Mackenzie class destroyer escorts from 1956-1997.  It had a water-cooled barrel and an automatic loader capable of delivering high rates of fire. 

Early development of the ammunition and gun barrel was a joint British-American project arising out the need for the US Navy to defend against Japanese Kamikaze attacks and was based on the 3”50 gun. However, the British style of mounting displayed was a unique design that was further modified and upgraded once in the hands of the RCN. Due to its long development period, the gun was removed from US warships after a short service life, while the British and Canadian Navies continued its use and made modifications. 

These guns were anti-aircraft with limited anti-surface warfare capabilities. Capable of firing 120 rounds per barrel per minute, reducing to 90 rounds per barrel per minute in service due to excessive barrel wear. Its range was 17.8 kilometres at 45 degrees and 11.5 kilometres at 90 degrees. It was considered "the ultimate anti-aircraft gun of the time". 

The original British mounting was prone to ammunition feed breakdowns and required considerable maintenance. Esquimalt became the centre for this maintenance as workers refitting ships would often remove pieces to be altered or completely replaced. When the ammunition handling system was working properly, it was referred to as "the bottling plant" due to its high rate of fire. 

Reference Links:
Naval Analyses - Warships of the Past
NavWeaps - 3"70 (7.62 cm) Mark 6