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16"/50 caliber Mark 7 gun
BB61 USS Iowa BB61 broadside USN.jpg
The Iowa-class battleship USS Iowa fires a full broadside of her 16"/50 Mark 7 guns.
Type Naval gun
Place of origin United States
Service history
In service 1943–1992
Used by US
Wars World War II
Korean War
Vietnam War
Lebanese Civil War
Gulf War
Production history
Designed 1939
Weight 267,904 lb (121,519 kg)
Length 68 ft (20.73 m)
Barrel length 66 ft 8 in/20.3 m (50 calibers)

Shell AP Mark 8: 2,700 lb. (1,225 kg)
HC Mark 13: 1,900 lb. (862 kg)
Nuclear Mark 23: 1,900 lb. (862 kg)
Caliber 16 in (406 mm)
Muzzle velocity AP: 2,500 ft/s (762 m/s)
HC & Nuclear: 2,690 ft/s (820 m/s)
Maximum range 23.64 mi (38 km)

The 16"/50 caliber Mark 7 – United States Naval Gun is the main armament of the Iowa-class battleships.


A cutaway of a turret mounting 16-inch guns

Due to a lack of communication during design, the Bureau of Ordnance assumed the Iowa class would use the 16"/50 Mark 2 guns constructed for the 1920 South Dakota-class battleships. However, the Bureau of Construction and Repair assumed that the ships would carry a new, lighter, more compact 16"/50 and designed the ships with barbettes too small to accommodate a 16"/50 Mark 2 triple turret. The new 16"/50 Mark 7 was designed to resolve this conflict.

These guns were 66.6 feet (20 m) long—50 times their 16-inch (406 mm) bore, or 50 calibers, from breechface to muzzle. Each gun weighed about 239,000 pounds (108,000 kg) without the breech, or 267,900 pounds (121,517 kg) with the breech.[1] They fired projectiles weighing from 1,900 to 2,700 pounds (850 to 1,200 kg) at a maximum speed of 2,690 feet per second (820 m/s) with a range of up to 24 miles (39 km). At maximum range the projectile spent almost 1½ minutes in flight.[1] Each turret required a crew of 94 men to operate.[1] The turrets themselves cost US$1.4 million each, to which the cost of the guns had to be added.[1]

The turrets were "three-gun", not "triple", because each barrel could be elevated and fired independently. The ships could fire any combination of their guns, including a broadside of all nine. The turret interiors were subdivided and so designed as to permit the independent loading, elevation and firing of each gun. Each turret was also installed with an optical range finder and ballistic analog computer. This permitted the turret’s gun captain and crew to locally engage targets, should battle damage disrupt communication with the ship’s primary or auxiliary fire control centers. Considering the large mass of the ship, compared to the mass of the projectiles, the ships barely moved sideways at all, even when a full broadside was fired. With the damping effect of the water around the hull the pressure wave generated by the gunfire was felt much more than the slight change in lateral velocity.[2]

The guns could be elevated from −5 degrees to +45 degrees, moving at up to 12 degrees per second. The turrets could rotate about 300 degrees at about 4 degrees per second and could even be fired back beyond the , which is sometimes called "over the shoulder". Within each turret, a red stripe on the wall of the turret, just inches from the railing, marked the boundary of the gun's recoil, providing the crew of each gun turret with a visual reference for the minimum safe distance range.[3]

Complementing the 16"/50 caliber Mark 7 gun was a fire control computer, in this case the Ford Instrument Company Mark 8 Range Keeper. This analog computer was used to direct the fire from the battleship's big guns, taking into account several factors such as the speed of the targeted ship, the time it takes for a projectile to travel, and air resistance to the shells fired at a target. At the time the Montana class was set to begin construction, the rangekeepers had gained the ability to use radar data to help target enemy ships and land-based targets. The results of this advance were telling: the rangekeeper was able to track and fire at targets at a greater range and with increased accuracy.[4] This gave the US Navy a major advantage in World War II, as the Japanese did not develop radar or automated fire control to the level of the US Navy.

Mark 8 "Super-heavy" shell

The Mark 7 gun was originally intended to fire the relatively light 2,240-pound (1,020 kg) Mark 5 armor-piercing shell. However, the shell-handling system for these guns was redesigned to use the "super-heavy" 2,700-pound (1,200 kg) APC (Armor Piercing, Capped) Mark 8 shell before any of the Iowa-class battleships were laid down. The large caliber guns were designed to fire two different 16 in (406 mm) shells: an armor piercing round for anti-ship and anti-structure work, and a high explosive round designed for use against unarmored targets and shore bombardment.

The Mark 7 guns and the 2,700-pound projectiles were 25 percent lighter than the 46 cm/45 Type 94 naval guns of the Japanese Yamato-class battleships, but had nearly the same armor penetration ability.[5]

The North Carolina and South Dakota classes could also fire the 2,700-pound Mark 8 shell, although with a shorter range, using the 16"/45 caliber Mark 6 gun. The Mark 6 gun was lighter than the Mark 7, which helped both battleship classes to conform to the limits of the Washington Naval Treaty.[6]

The Mark 8 shells gave the North Carolina, South Dakota, and Iowa classes the second heaviest broadside of all battleship classes, even though the North Carolina and South Dakota ships were treaty battleships. Only the Yamato-class super-battleships could throw more weight.

The propellant consists of small cylindrical grains of smokeless powder with an extremely high burning rate. A maximum charge consists of six silk bags, each filled with 110 pounds of propellant.[7]


Yard workers hoist one of nine 16"/50 Mark VII gun barrels aboard the USS Iowa during her construction in 1942.

The 16-inch/50 caliber Mark 7 guns of the forward turret of the battleship USS Wisconsin (BB-64) fires at enemy targets ashore on the Korean Peninsula on 30 January 1952 during the Korean War.

The built-up gun is constructed of liner, tube, jacket, three hoops, two locking rings, tube and liner locking ring, yoke ring and screw box liner. Some components were autofretted. Typical of United States naval weapons built in the 1940s, the bore was chromium plated for longer barrel life. It uses a Welin breech block that opens downwards and is hydraulically operated. The screw box liner and breech plug are segmented with stepped screw threads arranged in fifteen sectors of 24 degrees each.

Gun characteristics
Designation 16 in/50 caliber (406 mm × 20.3 m) Mark 7
Ship Class Used On Iowa (BB-61) and Montana (BB-67) classes
Date Of Design 1939
Date In Service 1943
Gun Weight 267,904 lb (121,519 kg) (including breech)
239,156 lb (108,479 kg) (without breech)
Gun Length oa 816 in (20.73 m) (breech face to muzzle)
Bore Length 800 in (20.32 m)
Rifling Length 682.9 in (17.35 m)
Grooves (96) 0.150 in deep (3.81 mm)
Lands N/A
Twist Uniform RH 1 in 25
Chamber Volume 27,000 cu in (0.44 m3)
Rate Of Fire 2 rounds per minute
Note: The primer cartridge can be either electric or percussion fired.
Range 41,622 yards (38.059 km or 20.55 nm) with nominal 660 lb (300 kg) powder charge
Muzzle Velocity 2,690 feet per second (820 m/s)

See also


  1. 1.0 1.1 1.2 1.3 DiGiulian, Tony (November 2006). "United States of America 16"/50 (40.6 cm) Mark 7". Archived from the original on 5 February 2007. Retrieved 25 February 2007. 
  2. Landgraff, R. A.; Locock, Greg. "Do battleships move sideways when they fire?". Archived from the original on 9 May 2008. Retrieved 19 May 2008. 
  3. "Mark 7 16-inch/50-caliber gun". Federation of American Scientists. Archived from the original on 11 March 2007. Retrieved 12 March 2007. 
  4. Clymer, A. Ben (1993). "The Mechanical Analog Computers of Hannibal Ford and William Newell" (pdf). IEEE Annals of the History of Computing. Massachusetts Institute of Technology. pp. 19–34. Retrieved 8 October 2011. 
  5. "16"/50 caliber Mark 7 gun". 2009. Retrieved 20 May 2012. 
  6. "USA 16"/45 (40.6 cm) Mark 6". 2009. Retrieved 8 October 2011. 
  7. Trainor, Bernard E. (23 April 1989). "Iowa Blast Inquiry: Long Search Ahead". The New York Times. Retrieved 8 October 2011. 

External links

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