Updated 15 April 2009

USS Connecticut B-18 getting one of her bow 12"/45 (30.5 cm) guns installed on 31 January 1906 at the New York Navy Yard

Bow turret on USS Conneticut B-18 during the Great White Fleet expedition
U.S. Naval Historical Center Photograph # NH 2400

Forward 12"/45 (30.5 cm) Turret of USS Mississippi B-23 in 1908
U.S. Naval Historical Center Photograph # 19-N-60-10-14

Another view of the forward turret on USS Mississippi B-23 in 1908
Note spotter towers and ventilation hatches
U.S. Naval Historical Center Photograph # NH 46043

Aft 12"/45 (30.5 cm) Turret of USS Mississippi B-23 in 1908
Note wing 8"/45 (20.3 cm) and 3-pdr guns in the superstructure
U.S. Naval Historical Center Photograph # 19-N-60-10-12

USS South Carolina B-26
The first US dreadnought and the first dreadnought anywhere with superfiring main-caliber turrets
U.S. Naval Historical Center Photograph # NH 44252

Breech of 12"/45 (30.5 cm) Mark 5 gun on USS North Dakota B-29
U.S. Naval Historical Center Photograph # NH 100784

Crew of Turret I on USS Utah B-31 in 1913
U.S. Naval Historical Center Photograph # NH 103835

USS New Hampshire B-25 firing on the target ship San Marcos (ex-Texas) at Tangier Sound in Chesapeake Bay, March 1911
This photograph is of historical interest as it was one of the first gun shoots where a spotter in the cage masts was used to spot fall of shot.  Previously, each gun layer or turret captain utilizing their turret gunsights was responsible.  This new technique increased the maximum possible engagement range from 12,000 yards (11,000 m) up to about 24,000 yards (22,000 m).
Also note the ship's wake and that firing a broadside did not push the ship sideways.
U.S. Naval Historical Center Photograph # NH 73105

12"/45 (30.5 cm) guns removed from scrapped battleships at the Philadelphia Navy Yard in December 1923
Many old battleships were scrapped as a result of the Washington Naval Limitation Treaty of 1921.  One of these guns is marked "Kansas", presumably indicating that it came from USS Kansas BB-21.  Ship being dismantled in the backround is USS South Carolina BB-26.
U.S. Naval Historical Center Photograph # NH 69035

28 August 2008 - Benchmark
15 April 2009 - Corrected date typographical error in caption for Connecticut bow gun