| 16"/50 caliber Mark 7 gun | |
|---|---|
The Iowa-class battleship USS Iowa fires a full broadside of her 16"/50 Mark 7 guns. |
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| Type | Naval gun |
| Place of origin | United States |
| Service history | |
| In service | 1943–1992 |
| Used by | United States |
| Wars | World War II Korean War Vietnam War Gulf War |
| Production history | |
| Designed | 1939 |
| Specifications | |
| Weight | 267,904 lb (121,519 kg) |
| Length | 68 ft (20.73 m) |
| Barrel length | 66 ft 8 in/20.3 m (50 calibers) |
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| 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.
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.
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These guns were 66 feet (20 m) long—50 times their 16-inch (410 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] Each turret cost US$1.4 million, but this figure did not take into account the cost of the guns themselves.[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 9. Contrary to popular belief, the ships did not move sideways when a broadside was fired.[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 beam, 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.
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-inch (410 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 North Carolina and South Dakota classes used the preceding 16"/45 caliber Mark 6 gun, which could fire the 2,700-pound shell. However, the Mark 6 had a shorter range, though this was unlikely to have been much of a disadvantage in battleship combat. The Mark 6 gun was lighter, which helped both battleship classes to conform to the limits of the Washington Naval Treaty.[5]
The Mark 7 guns and the 2,700-pound projectiles were 25 percent lighter than, and had 3/4 of the armor penetration ability as the 46 cm/45 Type 94 naval guns of the Japanese Yamato-class battleships.
The Mark 8 shells gave the North Carolina, South Dakota, and Iowa classes the second heaviest broadside of all battleship classes, despite the fact that 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.[6]
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.
| 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) |