3.7 inch anti-aircraft gun near the entrance to the secret wartime tunnels. This type of gun saw service throughout World War II with the United Kingdom, Australia, India, Canada and other commonwealth forces. The number of guns doubled from the start of the war to the Battle of Britain; some 1100 guns were employed by Summer 1940. Unlike the lighter and more mobile German 88mm dual purpose gun, the 3.7" wasn't employed as a tank killer because of command issues and lack of suitable anti-tank sights. It did serve as corps artillery in Italy in 1945.