The One O'Clock Gun is a time signal, fired every day at precisely 13:00, excepting Sunday, Good Friday and Christmas Day. The 'Time Gun' was established in 1861 as a time signal for ships in the harbour of Leith and the Firth of Forth, 2 miles (3 km) away. It complemented the 'Time Ball', which was installed on the Nelson Monument in 1852, but was useless as a visual signal in foggy weather. Because sound travels relatively slowly (approximately 343 metres per second (770 mph)), a map was produced in 1861 to show the actual time when the sound of the gun would be heard at various locations across Edinburgh.
The original gun was an 18-pound muzzle-loading cannon, which needed four men to load, and was fired from the Half Moon Battery. This was replaced in 1913 by a 32-pound breech-loader, and in May 1952 by a 25-pound Howitzer. The present One O'Clock Gun is an L118 Light Gun, brought into service on 30 November 2001. On Sunday 2 April 1916, the One O'Clock Gun was fired in vain at a German Zeppelin during an air raid, the gun's only known use in war.
The gun is now fired from Mill's Mount Battery, on the north face of the castle, by the District Gunner from the 105th Regiment Royal Artillery (Volunteers). Although the gun is no longer required for its original purpose, the ceremony has become a popular tourist attraction. The longest-serving District Gunner, Staff Sergeant Thomas McKay MBE, nicknamed "Tam the Gun", fired the One O'Clock Gun from 1979 until his retirement in January 2005. McKay helped establish the One O'Clock Gun Association, which opened a small exhibition at Mill's Mount, and published a book entitled What Time Does Edinburgh's One O'clock Gun Fire?. In 2006 Sergeant Jamie Shannon, nicknamed "Shannon the Cannon", became the 29th District Gunner, and in 2006 Bombardier Allison Jones became the first woman to fire the gun.
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