Caveat: The information contained in this post is of a very general nature. See references for where to find more detailed information. This post focuses on the 16″ naval guns and is not an overall evaluation of the Iowa-class battleships.
Let’s take a look at the guns that armed the last of the U.S. battleships. The U.S. 16″/50 Mark 7 is perhaps some of the best battleship main guns ever developed.
Development
As 1938 rolled around, the U.S. Navy began a series of design studies for “fast battleships” in the area of 45,000 tons displacement. Early studies by the General Board considered the use of the 18″/47 gun developed in the 1920s, however, the advantages that this weapon offered over the 16″/50 gun would’ve meant an increase in displacement beyond the 45,000-ton limit and the 16″ gun was considered better overall (Sumrall, 1988, p. 66). By May 1938, the General Board decided on a design that lead to the Iowa-class. This left the question of which Mark version of the 16″/50 gun to use. The resulting confusion, hilarity, and headaches offer a lesson in the importance of clear bureaucratic and departmental communication.
The problem was that the Bureau of Ordnance (BuOrd) based their turret design sketches off of the older 16″/50 Mk. 2 guns. These were relics of a WWI building program and many of these guns were still available. It should be noted that the barbette diameter for these turrets measured at 39’4″. In contrast, the Bureau of Construction and Repair (BuC&R) based their overall designs of the ship on the barbette for the Mk. 7 guns which had a diameter of 37’3″. In other words, the guys responsible for the guns designed a turret that was too big to fit into the spaces designed by the guys responsible for the ship. This mistake was not discovered until almost 6 months later!
Have you ever tried to fit a round peg into a hole that’s too small for it? Doesn’t work out too well, does it?
Thankfully, in December 1938, the BuOrd was able to rectify the situation and the design was changed so that the Mark 7 guns were fitted into turrets that were installed into the 37’3″ barbettes. However, this did result in a tight design and created some maintenance difficulties (Garzke & Dulin, 1976, p. 112-114).
Originally designed to fire the lighter 2,240 lb AP Mark 5 projectile, the shell handling system was redesigned to accommodate the heavier 2,700 lb AP Mark 8. These heavier projectiles allowed the guns to nearly equal the penetrating power of the Japanese 18.1″ guns for less weight (DiGiulian, 2019).
The 16″/50 Mark 7 guns were significantly more powerful than the previous 16″/45 Mark 6 versions on earlier battleships. The longer barrel and heavier propellant charge created increased muzzle velocity, longer range, and better armor penetration (Garzke & Dulin, 1976, p. 137).
In 1969, Capt. Edward Snyder of the USS New Jersey reported that the armor piercing shell could penetrate 32 ft of reinforced concrete (Garzke & Dulin, 1976, p. 137). Reportedly, the explosion of a High Capacity shell would create a crater 50 feet wide and 20 feet deep. Further reports during the Vietnam War note the New Jersey firing High Capacity shells to create helicopter landing zones 200 yards in diameter with the blast defoliating trees for 300 yards beyond that. Modernization in the 1980s included a DR-810 radar mounted on the turrets which aided in calculating muzzle velocity more accurately. Along with better powder consistency in the propellants and the Mark 160 Fire Control System, these became the most accurate battleship guns ever produced (DiGiulian, 2019).
Gun Characteristics
| Ship Class Used On: | Iowa & Montana (planned) -class battleships |
| Date In Service: | 1943 (Designed: 1939) |
| Gun Weight: | 267,904 lbs (121,515 kg) w/breech |
| Gun Length (overall): | 831.9 in (21.13 m) |
| Bore Length: | 68 ft (20.73 m) |
| Twist: | uniform RH 1 in 25 |
| Chamber Volume: | 27,000 cu in (442.451 L) |
| Rate of Fire: | 2 rounds/minute |
The guns were of a built-up construction consisting of a liner, A tube, jacket, three hoops, two locking rings, tube and liner locking ring, yoke ring, and screw box liner. Some components were autofretted. The bores were also chromium-plated to increase barrel life. The breech was a hydraulically operated Welin breech block that opened downwards. The screw box liner and breech plug were segmented with stepped screw threads arranged in fifteen sectors of 24 degrees each. (DiGiulian, 2019). To assemble the guns, each piece is heated and expanded before being slid into place over the tube. As they cool and shrink, a tight unit is created. The liner is inserted from the breech end in an electric shrink pit, and the locking ring prevents expansion aft when the gun is fired. The guns themselves are mounted in the turret in individual slides and can elevate independently of each other. Thus, they are three-gun turrets, rather than triple turrets. (Sumrall, 1988, p. 66-68).
Mount Characteristics
| Weight: | 1,701-1,708 tons (1,728.4- 1,735.4 mt) |
| Elevation: | -5 to +45 degrees |
| Elevation Rate: | 12 degrees/second |
| Train: | -150 to +150 degrees |
| Train Rate: | 4 degrees/second |
| Recoil: | 4 ft (1.219 m) |
| Loading Angle: | +5 degrees |
| Armor Thickness: | 17.0″ Class B armor over 2.5″ STS face; 9.5″ Class A armor over 0.75″ STS sides; 12.0″ Class A armor over 0.75″ STS rear; 7.25″ Class A armor over 0.75″ STS roof |
(Photo credit: OP-769, 1967, p. 1-2)
(Photo credit: OP-769, 1967, p. 2-4)
Each turret assembly consists of a gun house with a rotating structure, a fixed structure, a barbette, and magazines. The gun house is the rotating armored structure that contains the guns, sighting, and rangefinder stations. The gun pit and machinery flat extend below the shelf plate of the gun house into the upper and lower barbettes. Extending beneath the machinery flat to the turret foundation are two projectile handling flats, each with its own machinery for moving the shells. As Turret II is one deck higher than Turrets I and III, it contains an additional fixed handling flat below the upper and lower handling flats. The powder handling room is at the base beneath the shell handling flats (Sumrall, 1988, p. 69-70). A minimum of 77 men were required for the operation of each turret (Garzke & Dulin, 1976, p. 139).
Ammunition Types
AP: Armor Piercing HC: High Capacity i.e. high explosive HE-CVT: High Explosive - Controlled Variable Time ICM: Improved Conventional Munition (anti-personnel) HE-ET/PT: High Explosive - Electronic Time/Point Detonating
| Type: | Bag |
| Projectile Types & Weights: | (WWII & Korea) AP Mark 8: 2,700 lbs (1,224.7 kg) HC Mark 13 & 14: 1,900 lbs (861.8 kg) (1950s Deployments) Nuclear Mark 23: 1,900 lbs (862 kg) (1980s & 90s Deployments) HE-CVT Mark 143: 1,900 lbs. (862 kg) ICM Mark 144: 1,900 lbs. (862 kg) HE-ET/PT Mark 145: 1,900 lbs. (862 kg) |
| Bursting Charge: | AP Mark 8: 40.47 lbs (18.357 kg) HC Mark 13 & 14: 153.58 lbs (69.662 kg) Nuclear Mark 23: W23 warhead, ~15-20 kilotons HE-CVT Mark 143: probably the same as HC ICM Mark 144: 400 M43A1 anti-personnel grenades with time-fuzes HE-ET/PT Mark 145: similar to Mark 143 |
| Projectile Length: | AP Mark 8: 72.0 in (182.9 cm) HC Mark 13: 64.0 in (162.6 cm) HC Mark 14: 64.0 in (162.6 cm) Nuclear Mark 23: 64.0 in (162.6 cm) HE-CVT Mark 143: 64.0 in (162.6 cm) ICM Mark 144: 64.0 in (162.6 cm) HE-ET/PT Mark 145: 64.0 in (162.6 cm) |
| Propellant Charge: | (both full and reduced charges used six bags) WWII Full Charge: 660.0 lbs. (299.4 kg) WWII Reduced Charge: 305.0 lbs. (138.3 kg) WWII Reduced Flashless Charge: 325.0 lbs. (147.4 kg) Post WWII Full Charge: 655.0 lbs. (297.1 kg) Post WWII Reduced Charge: 305.0 lbs. (138.3 kg) Post WWII Reduced Flashless Charge: 325.0 lbs. (147.4 kg) |
| Muzzle Velocity: | AP: 2,500 fps (762 mps) (new gun) AP: 2,425 fps (739 mps) (average gun) AP: 1,800 fps (549 mps) (reduced charge) HC: 2,690 fps (820 mps) (new gun) HC: 2,615 fps (797 mps) (average gun) HC: 2,075 fps (632 mps) (reduced charge) |
| Working Pressure: | 18.5 tons/sq. in (2,910 kg/sq. cm) |
| Barrel Life: | ~290 rounds |
| Ammo stowage/gun | ~130 rounds (depending on turret and source used) |
In the 1960s, full propellant charges were given “Swedish additive” jackets which were filled with 4 pounds of titanium dioxide and wax. These were wrapped around the six powder bags and created an insulating layer that significantly reduced bore wear during firing. It’s estimated that four AP rounds (or nine HC rounds) fired with these jackets equaled the wear of a single AP round without the additive. During Vietnam, the New Jersey fired 6,222 rounds of 16″ ammo at both full and reduced charges and still estimated that 55% of the barrel life remained (Garzke & Dulin, 1976, p. 139).
Shells could be transferred between the turrets via an overhead monorail system in the main fore-and-aft passageway known as “Broadway”. The shells were moved by the monorail from Turret I and II, around the starboard side of Turret II to Broadway, and then aft to Turret III (Sumrall, 1988, p. 76).
The AP Mark 8 Shell
The AP (Armor Piercing) Mark 8 shell was adopted in mid-1939. It weighs 2,700 pounds with a Mark 21 Base Detonating Fuse (BDF) with a 0.033-sec delay and a 1.5% bursting charge. Fuse activation requires a resistance of 1.5″ of armor at 0 degrees obliquity or 0.375″ at 65 degrees obliquity (Sumrall, 1988, p. 73).
Full powder charges of 660 lbs give the shell a muzzle velocity of 2,500 fps. Special and reduced charges give muzzle velocities of 2,300 fps and 1,800 fps respectively. These give steeper angles of fall and a similar trajectory to the 16″/45 gun. They also reduce bore wear. Tactically, the reduced charges would allow the battleship to reduce a target’s immunity zone or enhance defilade capabilities against land targets (Sumrall, 1988, p. 73).
The HC Mark 13 Shell
Originally designated the EX-1, the High Capacity shell was introduced in late-1942. A high explosive shell, it weighs 1,900 lbs and can be fused with either the Mark 29 Point Detonating Fuse (PDF) or the Mark 48 BDF with a 0.15-sec delay. It has an 8.1% bursting charge. At full charge, the shell has a muzzle velocity of 2,690 fps (Sumrall, 1988, p. 73-74). The Mark 14 is identical except for the manufacturer (DiGiulian, 2019).
The Mark 23 “Katie” Nuclear Shell
Developed in the early-1950s, this nuclear 16″ shell carried the W23 warhead with a yield in the 15-20 kiloton range. Reportedly, these were modified Mark 13 shells and they weighed 1,900 lbs (Sumrall, 1988, p. 74).
Fifty of these shells were produced. The Iowa, New Jersey, and Wisconsin had Turret II altered with a secure storage area that could house 10 nuclear shells with 9 practice shells. With the exception of some practice shells, none were fired and the Navy has never confirmed whether or not the battleships ever carried nuclear devices. These shells were decommissioned by October 1962 (DiGiulian, 2019).
The HE-CVT Mark 143 Shell
This shell uses the Army M732 Controlled Variable Time (proximity) fuse (Sumrall, 1988, p. 74).
The ICM Mark 144 Shell
This is fused with an M724 Electronic Time Fuze (ETF). It dispenses 400 M43A1 wedge grenades (Sumrall, 1988, p. 74).
The HE-ET/PT Mark 145 Shell
Similar to the Mark 143, but uses the M724 ETF or point detonating fuses (Sumrall, 1988, p. 74).
Range & Armor Penetration
Note on Armor Penetration Values:
Garzke and Dulin (1976) derived the penetration values from “a detailed U.S. Navy empirical equation” modeled against U.S. Class B Homogeneous armor. The values are noted as not being precisely correct but should give an accurate measure of performance (p. 223). For a further examination of the Garzke and Dulin data, see the following article: The Garzke and Dulin Empirical Formula for Armor Penetration.
| Shell Type | AP (2,700 lbs) | Average | Reduced Charge | HC (1,900 lbs) | Reduced Charge |
| Muzzle Velocity | 2,500 fps (762 mps) | 2,425 fps (1,739 mps) | 1,800 fps (549 mps) | 2,690 fps (820 mps) | 2,075 fps (632 mps) |
| Range @ 10 deg | 17,650 yds (16,139 m) | 18,200 yds (16,642 m) | |||
| Range @ 15 deg | 23,900 yds (21,854 m) | 24,100 yds (22,037 m) | |||
| Range @ 20 deg | 29,000 yds (26,518 m) | 28,800 yds (26,335 m) | |||
| Range @ 25 deg | 33,300 yds (30,450 m) | 32,700 yds (29,901 m) | |||
| Range @ 30 deg | 36,700 yds (33,558 m) | 36,000 yds (32,918 m) | |||
| Range @ 35 deg | 39,500 yds (36,119 m) | 38,650 yds (35,342 m) | |||
| Range @ 40 deg | 41,430 yds (37,884 m) | 40,185 yds (36,745 m) | 40,600 yds (37,163 m) | ||
| Range @ 45 deg | 42,345 yds (38,720 m) | 24,181 yds (22,112 m) | 41,622 yds (38,059 m) | 27,350 yds (25,009 m) |
| Range | Armor Penetration (side plates) | Deck | Striking Velocity | Angle of Fall |
| 0 yds | 32.62″ (829 mm) | 2,500 fps (762 mps) | 0 | |
| 5,000 yds (4,572 m) | 29.39″ (747 mm) | 0.67″ (17 mm) | 2,280 fps (695 mps) | 2.5 deg |
| 10,000 yds (9,144 m) | 26.16″ (664 mm) | 1.75″ (43 mm) | 2,074 fps (632 mps) | 5.7 deg |
| 15,000 yds (13,716 m) | 23.04″ (585 mm) | 2.79″ (71 mm) | 1,893 fps (577 mps) | 9.8 deg |
| 20,000 yds (18,288 m) | 20.04″ (509 mm) | 3.90″ (99 mm) | 1,740 fps (530 mps) | 14.9 deg |
| 25,000 yds (22,860 m) | 17.36″ (441 mm) | 5.17″ (131 mm) | 1,632 fps (497 mps) | 21.1 deg |
| 30,000 yds (27,432 m) | 14.97″ (380 mm) | 6.65″ (169 mm) | 1,567 fps (478 mps) | 28.25 deg |
| 35,000 yds (32,004 m) | 12.97″ (329 mm) | 8.48″ (215 mm) | 1,555 fps (474 mps) | 36 deg |
| 40,000 yds (36,576 m) | 11.02″ (280 mm) | 11.26″ (286 mm) | 1,607 fps (490 mps) | 45.47 deg |
| 42,345 yds (38,720 m) | 9.51″ (241 mm) | 14.05″ (357 mm) | 1,686 fps (514 mps) | 53.25 deg |
Evaluation
As with any large caliber gun, the 16″/50 guns created significant blast pressure when they fired as the photos of the massive fireballs produced indicate. Reports indicate that blast pressures were measured at 50 psi when close to the muzzle and 7 psi up to 50 feet away. During a shore bombardment off Korea in March of 1951, the Missouri‘s guns “split vent ducts and welds, fractured the deck in two places, loosened teak plans, and did superficial injury to the hull structure and fittings in the vicinity of turret No. 3.” During a trial shoot in April of 1968, New Jersey‘s guns blew apart an accommodation ladder near the aft turret and blew life rafts out of their racks. Several observers also lost their hats overboard. Interestingly, sailors opined that the blast from the 5-inch secondary guns was harsher than the main battery. One sailor compared the two experiences of the 16″ and 5″ guns firing as (for the 16″ guns) “like being hit by a slow truck wrapped in sofa cushions. The 5-inchers, damn them, hit you like a plank” (Muir, 1987, p. 38 – 39). Much of the discomfort (and injury) has to do with where a sailor was in relation to the muzzle of the weapon being fired. Since the nearby decks were cleared when the main battery was fired, the concussion from the 16″ guns was probably felt much less by any exposed personnel. In contrast, the report of the 5″ guns, particularly when they were pointed skyward, was much more apparent to any crew standing in the superstructure since they were nearer to the muzzles of those guns. In fact, there have been several cases of men being injured by the concussive crack of a 5-inch gun, as opposed to the boom of a 16-inch gun. Ouch!
Ultimately, the 16″/50 guns could be considered some of the best battleship guns ever produced. Considering their relatively lightweight and the fact that larger guns have been produced, the main battery guns on the Iowa-class possessed impressive striking power.
Garkze and Dulin (1976) opine that while the Japanese 18.1″ guns fired a heavier shell at greater muzzle velocities, for all intents and purposes, the U.S. 16″ Mark 7 gun could match its penetration performance. This was because the American 16″ AP 2,700 lb shell had greater relative frontal density in terms of average weight per unit of cross-sectional area (p. 203). Since they never actually engaged each other, we can only speculate about the outcome of a clash between an Iowa and a Yamato battleship, the reality is that any number of factors besides the power of the guns would have come into play.
Perhaps what is most telling of the usefulness of the Iowa battleships and their main guns occurred on the doctrinal level. Whereas factions in the Imperial Japanese Navy hopelessly clung to the notion of battleships playing a key role in a potentially decisive naval battle, the U.S. Navy largely relegated the fast battleships to escort roles for aircraft carriers. Furthermore, the main battery guns of the battleships (in general) demonstrated their use by supporting amphibious assaults with shore bombardment missions. Indeed, there was only a handful of battleship vs. battleship encounters during the entirety of WWII in all theaters.
When the smoke from WWII had cleared, it appeared that the battleship had largely gone the way of the dinosaur. However, whereas most other battleships were either sunk or sent to the breakers, the Iowas remained floating to be occasionally brought back into service when called for.
Further post-WWII technological improvements in the projectiles, powder charges, and fire control lent credence to the argument that these battleships and their guns were still useful in an age of increasing automation and longer over-the-horizon capabilities with missiles. There is still something of a debate over the need for powerful battleship guns to support amphibious operations, but the increasing range and digitization of warfare appear to be calling for scalpel-like precision rather than sheer brute force. At the very least, we have the post-WWII performance of the 16″/50 Mark 7 guns in Korea, Vietnam, Lebanon, and Iraq for further evidence of their capabilities. In any case, it’s highly unlikely that these guns will ever be fired again given that all of the Iowa-class battleships now serve as museum ships.
References
DiGiulian, T. (2019). 16″/50 (40.6cm) Mark 7. Retrieved from http://www.navweaps.com/Weapons/WNUS_16-50_mk7.php
Garzke, W.H., & Dulin, R.O. (1976). Battleships: United States Battleships in World War II. Annapolis, MD: Naval Institute Press.
Muir, M. (1987). The Iowa Class Battleships. New York, NY: Sterling Publishing Co.
Naval Ordnance Systems Command. (1967, Nov. 1). NAVORD OP-769 16-Inch Three Gun Turrets BB 61 Class. Retrieved from https://eugeneleeslover.com/AMMUNITION/NAVORD-OP-769-TITLE-AND-FORWARD.html.
Sumrall, R.F. (1988). Iowa Class Battleships: Their Design, Weapons & Equipment. London, UK: Conway Maritime Press.
Fair Winds & Following Seas 