More powerful than the 16"/45 (40.6 cm) Mark 6 guns used on the North Carolina (BB-55) and South Dakota (BB-57) classes, this was possibly the best battleship gun ever put into service. Originally intended to fire the relatively light 2,240 pound (1,016.0 kg) AP Mark 5 projectile, the shell handling system for these guns was redesigned to use the "super-heavy" 2,700 pound (1,224.7 kg) AP Mark 8 before any of the USS Iowa class (BB-61) battleships were laid down. This heavier projectile made these guns nearly the equal in terms of penetration power to the 46 cm (18.1") guns of the Japanese Yamato class battleships, yet they weighed less than three-quarters as much.
As modernized in the 1980s, each turret carried a DR-810 radar that measured the muzzle velocity of each gun, which made it easier to predict the velocity of succeeding shots. Together with the Mark 160 FCS and better propellant consistency, these improvements made these weapons into the most accurate battleship-caliber guns ever made. For example, during test shoots off Crete in 1987, fifteen shells were fired from 34,000 yards (31,900 m), five from the right gun of each turret. The pattern size was 220 yards (200 m), 0.64% of the total range. 14 out of the 15 landed within 250 yards (230 m) of the center of the pattern and 8 were within 150 yards (140 m). Shell-to-shell dispersion was 123 yards (112 m), 0.36% of total range.
The Armor Piercing (AP) shell fired by these guns is capable of penetrating nearly 30 feet (9 m) of concrete, depending upon the range and obliquity of impact. The High Capacity (HC) shell can create a crater 50 feet wide and 20 feet deep (15 x 6 m). During her deployment off Vietnam, USS New Jersey (BB-62) occasionally fired a single HC round into the jungle and so created a helicopter landing zone 200 yards (180 m) in diameter and defoliated trees for 300 yards (270 m) beyond that.
A persistent anecdote is that the Iowa class suffered from alignment problems until after the Battle of Leyte Gulf. William Jurens, a noted expert on US naval weaponry, together with Iowa crewmembers and the staff at NSWC Dahlgren, performed a search of the official records for detailed data on this specific problem, but could find nothing in the files suggesting that the alignments were in any way out of the ordinary. Mr. Jurens' suspicion is that there may have been an oblique reference to an alignment problem in some document that was taken out of context; perhaps they were waiting for parts.
The Iowa class battleships are the sole survivors of the battleship era that can still be placed into service, although they now exist mainly as memorials.
The weapon is constructed of liner, A tube, jacket, three hoops, two locking rings, tube and liner locking ring, yoke ring and screw box liner. Some components were autofretted. As typical of USN weapons built in the 1940s, the bore was chromium plated for longer barrel life. Uses a hydraulically operated Welin breech block which opens downwards. The screw box liner and breech plug are segmented with stepped screw threads arranged in fifteen sectors of 24 degrees each.
|Designation||16"/50 (40.6 cm) 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 lbs. (121,519 kg) (including breech)
239,156 lbs. (108,479 kg) (without breech)
|Gun Length oa||816 in (20.726 m) (breech face to muzzle)|
|Bore Length||800 in (20.320 m)|
|Rifling Length||682.86 in (17.344 m)|
|Grooves||(96) 0.150 in deep (3.81 mm)|
|Twist||Uniform RH 1 in 25|
|Chamber Volume||27,000 in3 (442.5 dm3)|
|Rate Of Fire||2 rounds per minute|
- The primer cartridge can be fired either electrically or by percussion. The cartridge is automatically ejected when the breech opens after firing. In the case of a misfire, the cartridge can be manually removed and replaced without opening the breech.
- The bore was chromium plated for a distance of 690 inches (17.526 m) from the muzzle.
- Projectile travel was 689.67 in (17.518 m) (new gun).
- Air purging was used on these guns in order to quench and remove smoldering particles as a preventative measure against flareback. In movies or pictures, this purging can be seen as a small puff of white smoke that is emitted a few seconds after the gun fires.
|Projectile Types and Weights||World War II and Korean War Deployments
AP Mark 8 Mods 0 to 8 - 2,700 lbs. (1,225 kg) 1a 2a
HC Mark 13 Mods 0 to 6 - 1,900 lbs. (862 kg) 3a
HC Mark 14 Mod 0 - 1,900 lbs. (862 kg)
Target Mark 9 - 2,700 lbs. (1,225 kg) 4a
Target Mark 15 - 1,900 lbs. (861.8 kg) 5a
Target Mark 16 - 1,900 lbs. (861.8 kg)
Added during 1950s Deployments
|Bursting Charge||AP Mark 8 - 40.9 lbs. (18.55 kg)
HC Mark 13 - 153.6 lbs. (69.67 kg)
HC Mark 14 - 153.6 lbs. (69.67 kg)
Nuclear Mark 23 - W23 warhead, about 15-20 kilotons
|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)
|Propellant Charge 9a 10a 11a||World War II Full Charge - 660.0 lbs. (299.4 kg) SPD 839
World War II Reduced Charge - 305.0 lbs. (138.3 kg) SPD 840 or SPDN
World War II Reduced Flashless Charge - 325.0 lbs. (147.4 kg) SPCG
Post World War II Full Charge - 655.0 lbs. (297.1 kg) D839
|Muzzle Velocity 12a||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)
|Working Pressure||18.5 tons/in2 (2,910 kg/cm2)|
|Approximate Barrel Life 13a||290 - 350 rounds|
|Ammunition stowage per gun 14a||About 130 rounds|
- ^Approved in June 1939, the AP Mark 8 projectile was originally designed as the longer, heavier "big brother" to the AP Mark 5 projectiles used for the 16"/45 (40.6 cm) guns carried by the Colorado (BB-45) class battleships. Like the Mark 5, the Mark 8 projectiles were designed to be used in long-range gun actions against Japanese ships ("Plan Orange") and for that reason they were to be fired at relatively low muzzle velocities and high gun elevations. These conditions would result in a steeper angle of fall in order to enhance their deck armor penetration capabilities. In almost all respects the 1939 design of the Mark 8 Mod 0 was very similar to the Mark 5 except for length. However, around the end of 1944 the improved Mark 8 Mod 6 version came out with significantly better hardening techniques which gave a noticeable improvement in penetration at impact angles of 35 degrees or so against thick face-hardened armor. This performance was so much better that BuOrd put out a memo stating that battleships were to return all previous Mods of this projectile as quickly as the Mod 6 became available for loading aboard ship. The Mod 6 had an even blunter, rounded AP body nose (with no point) to further enhance penetration against deck armor at high obliquity. The Mod 8 had a heavier cap, blunter nose and harder body from improved heat treating techniques. The AP Mark 8 has a radius of ogive of 144 inches (366 cm) or 9crh and leaves the barrel rotating at about 4,000 RPM. This round creates overpressures exceeding 50 psi (3.5 kg/cm2) close to the muzzle and 7 psi (0.5 kg/cm2) at a distance of 50 feet (15 m) from the muzzle. The Mark 21 Base Detonating Fuze (BDF) had a delay of 0.033 seconds. Fuze activation required a resistance equal to 1.5 inches (3.8 cm) of armor at 0 degrees obliquity or 0.375 inches (1 cm) at 65 degrees obliquity. AP projectile bodies are painted black. The nose color indicates burster type, with yellow denoting Explosive D. A narrow colored band below the nose indicates the splash color.
- ^The AP Mark 8 had a nominal 1.5 lbs. (0.68 kg) dye bag but this was allowed to be as large as 3.0 lbs. (1.36 kg) in order to bring underweight projectiles up to standard. The Iowa class was assigned the following dye colors:
USS Iowa - Orange
USS New Jersey - Blue
USS Missouri - Red
USS Wisconsin - Green
- ^The HC Mark 13 was originally designed for the Colorado (BB-45) class battleships, whose shell handling system limited the maximum projectile length to about 4 calibers. For standardization purposes, the Mark 13 was also issued to all newer battleships, even though their shell handling systems could have accommodated a longer, heavier projectile. This much-needed projectile was introduced in late-1942 and was originally designated as the EX-1. The explosive cavity in the Mark 13 has a relatively thick-wall with a fairly constant sidewall thickness, getting slightly thicker at the nose. It had somewhat less explosive weight in terms of percent than most foreign projectiles of World War II or even earlier USN HE projectiles, since it had as one of its requirements the ability to penetrate light armor and heavy concrete for shore bombardment purposes. The Mark 13 uses both base delay and nose contact fuzes for greater reliability under differing conditions, but can be used with only one fuze if desired. During World War II BuOrd developed AA shells for these guns which were standard HC rounds with a mechanical time fuze replacing the usual nose contact fuze. This meant that the gunnery crews could easily change the function of any HC shell on board by simply replacing the nose fuze. These AA shells do not appear to have been issued their own Mark number, as they seem to have been known simply as the HC Mark 13 AA round. Like the AP Mark 8, the HC Mark 13 projectile has a radius of ogive of 144 inches (366 cm) or 9crh. The Mark 14 is identical to the Mark 13, being simply a different designation assigned to indicate manufacturers other than the Naval Gun Factory. The Naval Surface Warfare Center - Crane Division located at Crane, Indiana, manufactured some HC projectiles in 1969 and these were designated as Mark 14, but they were otherwise identical to the Mark 13. HC projectile bodies are painted green. The nose color indicates burster type, with yellow denoting Explosive D.
- ^Target Mark 9 use blind loaded and plugged (BL&P) AP Mark 8 projectile bodies.
- ^Target Mark 15 and Mark 16 use blind loaded and plugged (BL&P) HC Mark 13 projectile bodies.
- ^A total of fifty Mark 23 "Katie" nuclear projectiles were produced during the 1950s with development starting in 1952 and the first service projectile being delivered in October 1956. It is possible that the W23 nuclear warhead used for this projectile may have been installed inside of an otherwise unaltered HC Mark 13 shell body, although one of the sources listed below says that the projectile was slightly smaller than the Mark 13. USS Iowa, USS New Jersey and USS Wisconsin had an alteration made to Turret II magazine to incorporate a secure storage area for these projectiles. USS Missouri was not so altered as she had been placed in reserve in 1955. This secure storage area could contain ten nuclear shells plus nine Mark 24 practice shells. These nuclear projectiles were all withdrawn from service by October 1962 with none ever having been fired from a gun. One projectile was expended as part of Operation Plowshare (the peaceful use of nuclear explosive devices) and the rest were deactivated. USS Wisconsin did fire one of the practice shells during a test in 1957. It is not clear whether or not any of the battleships ever actually carried a nuclear device onboard, as the US Navy routinely refuses to confirm or deny which ships carry nuclear weapons. At least one Mark 23 shell body still exists at the National Atomic Museum in Albuquerque, New Mexico, as can be seen in the photograph below.
- ^During the 1980s, several new projectile assemblies based upon the HC Mark 13 projectile body were developed or planned. Some of these were in service during the Gulf War (1990).
HE-CVT Mark 143
HC projectile with a Controlled Variable Time (CVT) fuze. Burster probably same as Mark 13, 153.5 lbs. (69.6 kg).
Anti-Personnel Improved Conventional Munition (ICM) Mark 144
Modified Mark 13 shell body, designed to dispense anti-personnel submunitions. Considered exceptionally effective against personnel, aircraft and other "soft" targets. Carried 400 M43A1 anti-personnel "Bouncing Betty" grenades with time-fuzes.
HE-ET/PT Mark 145
Similar to Mark 143, but with Electronic-Time (ET) and Point-Detonating (PD) fuzes.
Anti-Personnel ICM Mark 146 (Planned)
Similar to Mark 143, but contained 666 M42/M46/M77 SADARM bomblets with time-fuzes. Does not appear to have entered service.
Improved HC Mark 147? (Planned)
During the battleship reactivations during the 1980s, the Navy developed a new HC design that was the same length as the AP Mark 8 (4.5 calibers) and weighed 2,240 lbs. (1,015 kg). Several of these were test-fired from USS Iowa and at Dahlgren, achieving ranges over 51,000 yards (46,600 m) with a new gun muzzle velocity of 2,825 fps (861 mps). This projectile does not appear to have entered general service use before all of the battleships were decommissioned in the early 1990s. The "Mark 147" designation is my guess, I would be interested in learning the exact designation and any other relevant details about this projectile.
HE-ER Mark 148 (Planned)
13.65 in (34.7 cm) diameter, extended-range (ER), sub-caliber projectile with sabot. Length was approximately 72 in (183 cm). Projectile was to be ET-fuzed with a payload of about 300 M48 grenade submunitions. Experiments with this projectile were conducted during the 1980s, but development was cancelled in FY91 when the battleships were decommissioned. Projectile weight without the sabot was about 1,300 lbs. (590 kg) and range was to be in excess of 70,000 yards (64,000 m) at a muzzle velocity of 3,600 fps (1,097 mps). See photograph below.
HE-ER Mark ? (Planned)
Advanced Gun Weapon Systems Technology Program 16/11-Inch Long Range GPS Concept with Sabot.
Another sub-caliber projectile with sabot, this one 11 inches (28 cm) in diameter. This project was also cancelled about FY91.
A sketch of this projectile may be seen below.
Data below courtesy of United States Naval Fire Support Association (USNFSA):
Range: 100 nm
Launch Weight: 650 lbs. (295 kg)
Fly Away Weight: 525 lbs. (238 kg)
Launch Length: 69 in (175 cm)
Payload: 248 M46 Submunitions, total weight of 175.2 lbs. (79.5 kg)
Guidance Modes: GPS and INS
- ^A 1981 inventory of naval ammunition storage facilities found that there were 15,500 HC projectiles, 3,200 AP projectiles and 2,300 practice rounds in stock.
- ^The propellant was in six bags for both full and reduced charges. Propellant bags were made from raw silk, although rayon may have been introduced during the 1980 activations. Primer patch was at one end, quilted to ensure even distribution, and usually colored red. The other end had a handling strap. Bags were transferred from hoist to loading tray three bags at a time and then all six bags were rammed into the breech with a single stroke. During the 1980s reactivations, some experiments were performed using five bag loads.
- ^The D839 propellant grain used for full charges originally issued for this gun was 2 inches long (5.08 cm), 1 inch in diameter (2.54 cm) and had seven perforations, each 0.060 inches in diameter (0.152 cm) with a web thickness range of 0.193 to 0.197 inches (0.490 to 0.500 cm) between the perforations and the grain diameter. In addition to the propellants listed above, Reduced Charges for Target rounds were made with 340 lbs. (154 kg) of SPDN and 325 lbs. (147 kg) of SPCG. Full and AP Target charges were stacked while Reduced charges were dumped.
- ^During the 1980 deployments, D846, originally manufactured for the 16"/45 (40.6 cm) Mark 6 guns, was issued for use with the 1,900 lbs. (861.8 kg) HC projectiles. The charge weight was 571 lbs. (259 kg) for a MV of 2,690 fps (820 mps). Testing was also performed with rebagged 8" (20.3 cm) propellant for HC reduced charges. This gave good accuracy and predictable performance, but it was not put into service use.
- ^When the smokeless propellants (SP) were freshly made during World War II, MV varied no more than +/- 10 fps (3 mps) shot to shot and often no worse than +/- 5 fps shot to shot. As SP will degrade over time, a few years later during the Korean deployments MV varied about +/- 14 fps (4.3 mps) and during Vietnam about +/- 23 fps (7 mps). By the time of the 1980s deployments, shot to shot variation was about +/- 32 fps (9.8 mps). This large variation was a primary contributor to USS New Jersey's poor shooting off Lebanon in 1984. As a result, the NSWC Dhalgren facility and USS Iowa were tasked with improving performance. Old D839 and D846 propellant lots were remixed and proved to bring variation back within the +/- 10 fps requirement.
- ^When first introduced into service during World War II, the barrel life was 290 ESR, the lower of the two values given above. At that time, Smokeless Powder Diphenylamine (SPD) was the standard propellant. HC rounds at 2,690 fps (820 mps) were 0.43 ESR and at 1,900 fps (579 mps) were 0.03 ESR. The Target rounds at 1,800 fps (549 mps) were 0.08 ESR. A slight reduction in charge weight raised liner life to 350 ESR by the start of the Korean War. In the 1967 and 1980s deployments, the use of "Swedish Additive" (titanium dioxide and wax) greatly reduced barrel wear. It has been estimated that four AP shells fired using this additive approximated the wear of a single AP shell fired without the additive (0.26 ESR) and that HC rounds fired with the additive caused even less wear (0.11 ESR). The "Swedish Additive" was issued in a packet that was inserted between two of the propellant bags. Later developments during the 1980s deployment led to putting a polyurethane jacket over the powder bags, which reduced the wear still further. This jacket was simply a sheet of foam with a fabric border around the ends that is tied to the powder bag. When the jacket burns during firing, a protective layer forms over the surface of the liner which greatly reduces gaseous erosion. This wear reduction program was so successful that liner life could no longer be rated in terms of ESR, as it was no longer the limiting factor. Instead, the liner life began to be rated in terms of Fatigue Equivalent Rounds (FER), which is the mechanical fatigue life expressed in terms of the number of mechanical cycles. The 16"/50 (40.6 cm) Mark 7 was ultimately rated at having a liner life of 1,500 FER.
- ^There are conflicting accounts about the number of rounds that could be carried by the Iowa class. Here are two sources that I consider creditable.
Projectile Stowage from OP 769 "16-Inch Three Gun Turrets BB-61 Class" Location Projectile Stowage Turret I Projectile Stowage Turret II Projectile Stowage Turret III Upper Projectile Flat Outer Ring 120 70 100 Lower Projectile Flat Outer Ring 126 125 126 Each of the two Inner Rings 72 72 72 Fixed Stowage, Third Level N/A 121 N/A Total 390 460 370 Grand Total 1,220
There were also 9 drill projectiles per turret for a total of 27.
OP 769 was first issued in 1943 and updated when USS New Jersey BB-63 was recommissioned in 1969.
The following projectile and powder canister numbers are taken from notes and sketches made by a chief gunner's mate for USS Missouri BB-63 just before she was decommissioned in February 1955.
Projectile Stowage from USS Missouri BB-63 Notes Turret Number 16-inch Projectiles 16-inch Powder Canisters Turret I 387 843 Mark 4 or 989 Mark 8 Turret II 456 928 Mark 4 or 1,148 Mark 8 Turret III 367 743 Mark 4 or 874 Mark 8 Total 1,210 2,514 Mark 4 or 3,011 Mark 8
Each Propellant Canister held three propellant bags. Mark 4 were Full Service Charges, Mark 8 were Reduced Service Charges.
As was typical of US designs, the higher position of Turret II allowed significantly more projectile stowage compared to the other two mountings.
Some powder magazines were converted to other purposes during the 1980s-1990s deployments, but the shell storage does not seem to have ever been reduced.
- In the spring or summer of 1967 when USS New Jersey (BB-62) was being activated for Vietnam, Indian Head Naval Ordnance Station proposed taking 23,000 non-nuclear 280 mm (11") shells left over from the Army's "atomic cannon" program and converting them via a sabot and obturator to be used in 16" (40.6 cm) guns. This was apparently a part of or in conjunction with the "Gunfighter" program for developing Long Range Bombardment Ammunition (LRBA) projectiles. Test shots were fired in 1968 and 1969 at Yuma and at Barbados, with the latter location using two 16"/45 (40.6) cm guns welded end-to-end and achieving ranges out to 83,850 yards (76,670 m) with a 745 lbs. (338 kg) shell fired at a muzzle velocity of 4,550 fps (1,387 mps). The program was apparently halted when New Jersey was decommissioned in 1969. A photograph of the disassembled saboted round is shown below. During the 1980s deployment, an investigation was undertaken to consider converting 280 mm projectiles into cargo rounds carrying about 300 sub-munitions, but no prototypes were constructed.
- All full-caliber projectiles have a bourrelet diameter of 15.977 inches (40.058 cm) and have two rear bourrelets, one on either side of the driving bands, to improve shot centering as the projectile exits the muzzle.
|Elevation||AP Mark 8||HC Mark 13|
|10 degrees||17,650 yards (16,139 m)||18,200 yards (16,642 m)|
|15 degrees||23,900 yards (21,854 m)||24,100 yards (22,037 m)|
|20 degrees||29,000 yards (26,518 m)||28,800 yards (26,335 m)|
|25 degrees||33,300 yards (30,450 m)||32,700 yards (29,901 m)|
|30 degrees||36,700 yards (33,558 m)||36,000 yards (32,918 m)|
|35 degrees||39,500 yards (36,119 m)||38,650 yards (35,342 m)|
|40 degrees||41,430 yards (37,884 m)||40,600 yards (37,163 m)|
|45 degrees||42,345 yards (38,720 m)||41,622 yards (38,059 m)|
- With reduced charges, the AP Mark 8 had a maximum range of 24,180 yards (22,110 m) while the HC Mark 13 had a maximum range of 27,350 yards (25,010 m).
- The Mark 23 Nuclear shell had about the same weight and ballistic shape as did the HC Mark 13 projectile and, as noted above, the nuclear warhead may have been installed in an otherwise unaltered Mark 13 shell body. For these reasons, I would assume that the elevation/range performance of the Mark 23 would be similar to that of the Mark 13. For the same reasons, the performances of the Mark 143, Mark 144 and Mark 145 projectiles should all be similar to that of the Mark 13.
- Time of flight for AP Shell with MV = 2,500 fps (762 mps)
10,000 yards (9,140 m): 13.2 seconds
20,000 yards (18,290 m): 29.6 seconds
30,000 yards (27,430 m): 50.3 seconds
36,000 yards (32,920 m): 66.1 seconds
40,000 yards (36,580 m): 80.0 seconds
- Time of flight for HC Shell with MV = 2,615 fps (797 mps)
10,000 yards (9,140 m): 13.1 seconds
20,000 yards (18,290 m): 30.3 seconds
30,000 yards (27,430 m): 53.2 seconds
35,000 yards (32,000 m): 70.3 seconds
39,500 yards (36,120 m): 86.0 seconds
- The maximum range with the originally planned 2,240 lbs. (1,016 kg) AP Mark 5 was 47,000 yards (42,980 m). Muzzle velocity would have been 2,700 fps (823 mps) with a charge of 640 lbs. (290 kg) SPD.
- At an "average gun" MV of 2,425 fps (1,739 mps), the maximum range with AP Mark 8 at a 40 degree elevation was 40,185 yards (36,745 m).
|Elevation||Time of Flight||Horizontal Range||Altitude||Slant Range|
|10 degrees||2||1,653 yards (1,512 m)||271 yards (248 m)||1,705 yards (1,559 m)|
|10 degrees||4||3,299 yards (3,017 m)||489 yards (447 m)||3,335 yards (3,050 m)|
|10 degrees||10||7,785 yards (7,119 m)||847 yards (774 m)||7,831 yards (7,161 m)|
|20 degrees||2||1,608 yards (1,470 m)||559 yards (511 m)||1,702 yards (1,556 m)|
|20 degrees||4||3,153 yards (2,883 m)||1,054 yards (964 m)||3,324 yards (3,039 m)|
|20 degrees||10||7,469 yards (6,830 m)||2,188 yards (2,001 m)||7,778 yards (7,112 m)|
|30 degrees||2||1,483 yards (1,356 m)||829 yards (758 m)||1,699 yards (1,554 m)|
|30 degrees||4||2,910 yards (2,661 m)||1,584 yards (1,448 m)||3,313 yards (3,029 m)|
|30 degrees||10||6,909 yards (6,318 m)||3,457 yards (3,161 m)||7,726 yards (7,065 m)|
|40 degrees||2||1,313 yards (1,201 m)||1,074 yards (982 m)||1,696 yards (1,551 m)|
|40 degrees||4||2,577 yards (2,356 m)||2,066 yards (1,889 m)||3,303 yards (3,020 m)|
|40 degrees||10||6,135 yards (5,610 m)||4,611 yards (4,216 m)||7,675 yards (7,018 m)|
|45 degrees||2||1,211 yards (1,107 m)||1,185 yards (1,084 m)||1,695 yards (1,550 m)|
|45 degrees||4||2,380 yards (2,176 m)||2,284 yards (2,088 m)||3,299 yards (3,017 m)|
|45 degrees||10||5,673 yards (5,187 m)||5,133 yards (4,694 m)||7,651 yards (6,996 m)|
- The above information is from OP 1091 "A.A. Range Table for 16-inch 50-caliber Gun" for a 1,900 lbs. (861.8 kg) HC round at a muzzle velocity of 2,615 fps (797 mps).
- Time of flight is in seconds. The time of flight in the range tables in OP 1091 go to the surface impact point, which is over a minute for elevations above 25 degrees, but I believe that the figures given in the table above would represent practical use against aircraft during World War II.
- Time fuzes were probably set by hand on the loading tray. HC rounds with VT fuzes were issued late in the war, but these may have been intended more for shore bombardment purposes rather than for AA defense.
|Range||Percentage hits against a broadside target||Percentage hits against an end-on target||Ratio|
|10,000 yards (9,144 m)||32.7||22.3||1.47:1|
|20,000 yards (18,288 m)||10.5||4.1||2.56:1|
|30,000 yards (27,432 m)||2.7||1.4||1.92:1|
- The above table is taken from page 98 (Table 21) of "Accuracy of Gunfire of the Main Batteries of United States Battleships" AMP Report No. 79.2R (SRG-P No. 48), produced in July 1944. This study estimated that an Iowa Class (BB-61) battleship firing with top spot against a target the size of an Iowa-class battleship would be expected to achieve the above hit percentages.
- Too much reliance should not be placed on these values, as figures such as these would have to be related to the precise conditions and spotting regime that was used during the calculation/experimentation process. For example, at 10,000 yards (9,100m) and 0 degrees target angle, the precise figures (using BB-61 as a target) would suggest hit percentages of 22.3% for 'Top Spot', 26.7% for 'Plane Spot' and 25.4% for 'Radar Spot' regimes.
- The data used to calculate these probabilities came from target practice shoots carried out by the battleships. As such, I would suspect that under actual battle conditions that these values would be on the optimistic side.
|Range||Side Armor||Deck Armor||Striking Velocity||Angle of Fall|
|0 yards (0 m)||32.62" (829 mm)||---||2,500 fps (762 mps)||0|
|5,000 yards (4,572 m)||29.39" (747 mm)||0.67" (17 mm)||2,280 fps (695 mps)||2.5|
|10,000 yards (9,144 m)||26.16" (664 mm)||1.71" (43 mm)||2,074 fps (632 mps)||5.7|
|15,000 yards (13,716 m)||23.04" (585 mm)||2.79" (71 mm)||1,893 fps (577 mps)||9.8|
|20,000 yards (18,288 m)||20.04" (509 mm)||3.90" (99 mm)||1,740 fps (530 mps)||14.9|
|25,000 yards (22,860 m)||17.36" (441 mm)||5.17" (131 mm)||1,632 fps (497 mps)||21.1|
|30,000 yards (27,432 m)||14.97" (380 mm)||6.65" (169 mm)||1,567 fps (478 mps)||28.25|
|35,000 yards (32,004 m)||12.97" (329 mm)||8.48" (215 mm)||1,556 fps (474 mps)||36.27|
|40,000 yards (36,576 m)||11.02" (280 mm)||11.26" (286 mm)||1,607 fps (490 mps)||45.47|
|42,345 yards (38,720 m)||9.51" (241 mm)||14.05" (357 mm)||1,686 fps (514 mps)||53.25|
The above information is from "Battleships: United States Battleships 1935-1992" for a muzzle velocity of 2,500 fps (762 mps) and is based upon the USN Empirical Formula for Armor Penetration. These values are in substantial agreement with armor penetration curves published in 1942.
|Range||Angle of Fall||Striking Velocity||Thickness in feet (meters) at an Obliquity of:|
|0 degrees||30 degrees|
|10,000 yards (9,144 m)||5.7||2,074 fps (632 mps)||27.5 (8.4)||20.5 (6.2)|
|15,000 yards (13,716 m)||9.8||1,892 fps (577 mps)||23.5 (7.2)||17.5 (5.3)|
|20,000 yards (18,288 m)||14.9||1,740 fps (530 mps)||21.0 (6.4)||15.5 (4.7)|
|25,000 yards (22,860 m)||21.1||1,632 fps (497 mps)||19.5 (5.9)||14.5 (4.4)|
|30,000 yards (27,432 m)||28.25||1,567 fps (478 mps)||18.5 (5.6)||14.0 (4.3)|
|35,000 yards (32,004 m)||36.0||1,556 fps (474 mps)||18.0 (5.5)||13.5 (4.1)|
|40,000 yards (36,576 m)||45.47||1,607 fps (490 mps)||19.0 (5.8)||14.0 (4.3)|
|42,345 yards (38,720 m)||53.25||1,686 fps (514 mps)||20.0 (6.1)||15.0 (4.6)|
The above information is from OP 1172 using a muzzle velocity of 2,500 fps (762 mps) (new gun). Reinforced concrete is specified as able to withstand a pressure of 5,000 psi (352 kg/cm2).
|Range||Angle of Fall||Striking Velocity||Thickness in feet (meters) at an Obliquity of:|
|0 degrees||30 degrees|
|10,000 yards (9,144 m)||5||2,083 fps (635 mps)||16.5 (5.0)||13.0 (4.0)|
|15,000 yards (13,716 m)||10||1,820 fps (555 mps)||14.0 (4.3)||11.0 (3.4)|
|20,000 yards (18,288 m)||16||1,606 fps (490 mps)||12.5 (3.8)||9.5 (2.9)|
|25,000 yards (22,860 m)||23||1,461 fps (445 mps)||11.0 (3.4)||8.5 (2.6)|
|30,000 yards (27,432 m)||32||1,391 fps (424 mps)||10.5 (3.2)||8.0 (2.4)|
|35,000 yards (32,004 m)||41||1,394 fps (425 mps)||10.5 (3.2)||8.0 (2.4)|
|40,000 yards (36,576 m)||51||1,479 fps (451 mps)||11.0 (3.4)||9.0 (2.7)|
|41,622 yards (38,060 m)||57||1,552 fps (473 mps)||12.0 (3.7)||9.5 (2.9)|
The above information is from OP 1172 using a muzzle velocity of 2,690 fps (820 mps) (new gun). Reinforced concrete is specified as able to withstand a pressure of 5,000 psi (352 kg/cm2).
Iowa (3) 1e and Montana (4)
|Weight||Iowa class: 1,701 - 1,708 tons (1,728.4 - 1,735.4 mt)
Montana class: N/A 2e
|Elevation||Turrets I and III: -2 / +45 degrees
Turret II: 0 / +45 degrees
|Rate of Elevation||12 degrees per second|
|Train 3e||1940s to 1950s
All Turrets: -150 / +150 degrees
1980s to 1990s
|Rate of Train||4 degrees per second|
|Gun Recoil 4e||47 in (119 cm)|
|Loading Angle||+5 degrees|
- ^The mountings for the Iowa class were originally to have used the same gun as planned for the never-built South Dakota BB-49 class, the 16"/50 (40.6 cm) Mark 2. In April of 1938, during a General Board review, BuOrd produced sketches for a standard turret using these guns and also showed a new, lightweight turret that would still use the 16"/50 Mark 2 guns. However, this lightweight turret was just a paper study, it was not a real design that BuOrd was actively studying. Not fully understanding this, the General Board selected the lightweight turret, but did not make this clear to the BuOrd representatives. As a result of this mistaken understanding, the ship designers of the Bureau of Construction and Repair (BuC&R) and BuOrd came away with different conclusions as to which turret would be used; the ship designers going with the lighter, smaller turret and BuOrd going with the heavier turret. This discrepancy was not found until November 1938, causing much consternation to all parties. Fortunately, BuOrd was able to quickly propose a smaller, lighter gun which became the 16"/50 Mark 7. These guns could use the lighter turret design and by the end of 1938 all parties were finally working on the same page. This new mounting was about the same size as the three-gun 16"/45 (40.6 cm) turrets used for the North Carolina BB-55 and South Dakota BB-57 classes, which meant that the turret training pinions were crowded together and difficult to access.
- ^The turrets for the Montana class would have been similar to those for the Iowa class, but with significantly thicker armor, so they would have been much heavier. See Armor note below.
- ^Training was by a 300 hp electric motor driving hydraulic gear. Each gun had a 60 hp motor for elevation, a 60 hp motor for ramming, a 75 hp motor for the shell hoist and a 100 hp motor for the powder hoist. Each shell ring was powered by a 40 hp motor. Training arcs were restricted during the 1980s activations in order to avoid overpressure problems to the new electronic and missile installations.
- ^The recoil distance given above is the nominal figure. The absolute, metal-to-metal recoil distance was 48 inches (122 cm). When the gun is fired with full charges at a +15 degree elevation, recoil lasts 0.43 seconds and counter recoil (runout) lasts 0.90 seconds. During runout, the gun is automatically lowered to the loading position, thus speeding up the firing cycle time.
- As built, all three turrets on the Iowa class had 25 power, 46 foot (14 m) rangefinders, with Stereoscopic Mark 52 used in Turrets II and III and Coincidence Mark 53 in Turret I. The Mark 52 weighs 10,500 lbs. (4,763 kg) and cost about $100,000 US during World War II. Near focus for the Mark 52 is 5,000 yards (4,570 m) and the maximum range is 45,000 yards (41,150 m). Mark 53 was a coincidence type with a special astigmatic lens which allowed it to range in on a single point source, such as a searchlight. In the 1950s, the Mark 53 rangefinder was removed from all four Iowa class battleships as weight compensation for growth in other areas. This rangefinder was selected as the increasing sophistication of fire control radar made its special capability redundant. The lower height of Turret I above the water also meant that this mounting had a shorter distance to the horizon capability. The openings in Turret I were then armor-plated over, as can be seen in the photographs below.
- Each turret requires about 94 men to operate, including the crew in the magazine and shell handling spaces.
- These mountings used delay coils, which delayed the firing of the guns by about 0.060 seconds (60 milliseconds). This delay, plus a wider spacing between the gun barrels than on the older ships, improved the dispersion patterns. The firing order was left, right, center. During the 1980s activations, agastats (time delay relays) were fitted to the right and left gun and these created a turret-whipping problem. This was corrected by increasing the delay in the right gun to 1 second. Wisconsin differed from her sisters in having a 1 second delay for the left gun and 2 seconds for the right gun.
- The gun axes are 122 in (310 cm) apart according to BuOrd OP 769. "Naval Weapons of World War Two" mistakenly says 117 in (297 cm), the same as this reference lists for the 16"/45 (40.6 cm) Mark 6 guns used on the North Carolina (BB-55) and South Dakota (BB-57) classes.
- These turrets cost about $1,400,000 each, not including the cost of the guns themselves.
- When inspected during the initial reactivation process in the 1980s, all twelve turrets on the four battleships of the Iowa class were found to be in excellent shape thanks to the care taken during their deactivations. The largest problem found was in the elevation power drives for two of the guns on USS Iowa (BB-61). These guns were unable to hold elevation and would oscillate around at the desired setting. Investigation of the historical records showed that the problem had existed at the time of her deactivation and that major repair efforts had been underway at that time. Repairs during the 1980s reactivation were hampered by the thirty-year hiatus since she was placed in reserve, as this meant that very few personnel were familiar with the complexities of the equipment. This necessarily meant that a long learning process was required to acquaint maintenance personnel with the equipment involved.
"Secondly, a preservative (cosmoline), which was used to preserve the equipment during deactivation, was a major problem that hindered the investigative work. The preservative, because of the long term deactivation period, had become hardened, making it difficult to remove. As the systems were reactivated and operated, this preservative would continually work loose. This material would then clog orifices, etc., in the Servo Control System causing erratic equipment operation which complicated the investigative process. Eventually, the source of the problem was pinpointed on both guns. For one of these guns, it meant the replacement of a major assembly - the A-end pump. The other gun was corrected by replacing a major sub-assembly and the fine adjustment of the regulator assembly" - from "Reactivation of 16-inch Three Gun Turrets in the Battleship."
Other than these two items on USS Iowa, it was found that the only other gunnery-related items requiring replacement were the breech closing control valves. Because of deterioration from age and use, all of the original valves were not able to hold pressure and so were replaced by a commercially available valve that was a direct replacement for the original one. Repair kits containing the new valves were added to the Naval supply system to ensure logistical support. To solve the problem with the preservative fouling the hydraulic systems, a large capacity 0.5 micron filter system with an integral motor/pump assembly was installed on each train and elevation unit during reactivation. These units worked continuously to filter the hydraulic fluid. This system was outside of the normal hydraulic system and operated even when the mountings were not in use, thus ensuring cleanliness of the hydraulic fluid.
- Armor thickness for the Iowa Class (BB-61) given in "Iowa Class Battleships" and "Battleships: United States Battleships, 1935 - 1992":
Face: 17.0 in (43.2 cm) Class B armor over 2.5 in (6.4 cm) STS
Sides: 9.5 in (24.1 cm) Class A armor over 0.75 in (1.9 cm) STS
Rear: 12.0 in (30.5 cm) Class A armor over 0.75 in (1.9 cm) STS
Roof: 7.25 in (18.4 cm) Class A armor over 0.75 in (1.9 cm) STS
Armor thickness for the Montana Class (BB-67) given in "Battleships: United States Battleships, 1935 - 1992":
Face: 18.0 in (45.7 cm) Class B armor over 4.5 in (11.4 cm) STS
Sides: 10.0 in (25.4 cm) Class A armor over 0.75 in (1.9 cm) STS
Rear: 12.0 in (30.5 cm) Class A armor over 0.75 in (1.9 cm) STS
Roof: 9.15 in (23.2 cm) Class A armor over 0.75 in (1.9 cm) STS
"Naval Weapons of World War Two" by John Campbell
"US Battleships: An Illustrated Design History," "US Naval Weapons" and "The Naval Institute Guide to World Naval Weapon Systems 1991/92" all by Norman Friedman
"The Iowa Class Battleships" by Malcolm Muir
"Battleships: United States Battleships, 1935 - 1992" by William H. Garzke, Jr. and Robert O. Dulin, Jr.
"Battleships" by Paul Stillwell
"Iowa Class Battleships" by Robert F. Sumrall
"Naval Ordnance and Gunnery - 1952" Navpers 16116-B
"U.S. Navy Bureau of Ordnance in World War II" by Lt. Cmdr. Buford Rowland, USNR, and Lt. William B. Boyd, USNR
"16-Inch Three Gun Turrets BB-61 Class: OP 769 - 30 April 1968" by Bureau of Ordnance (BuOrd), Department of the Navy
"16-Inch Range Table, 2,500 Initial Velocity to 42,345 Yards: OP 770 - October 1941" by Bureau of Ordnance (BuOrd), Department of the Navy
"A.A. Range Table for 16-inch 50-caliber Gun: OP 1091 - 11 March 1944" by Bureau of Ordnance (BuOrd), Department of the Navy
"Performance of Bombs and Projectiles against Shore Installations: OP 1172 - 9 May 1944" by Bureau of Ordnance (BuOrd), Department of the Navy
"U.S. Explosive Ordnance: OP 1664 - 28 May 1947" by Bureau of Ordnance (BuOrd), Department of the Navy
"Accuracy of Gunfire of the Main Batteries of United States Battleships" AMP Report No. 79.2R (SRG-P No. 48), produced in July 1944
"Reactivation of 16-inch Three Gun Turrets in the Battleships" by Art Romano, Naval Sea Systems Command
"Sympathetic Detonation of 16"/50 HC Projectiles" by Michael M. Swisdak, Jr. and Francis B. Porzel, Naval Surface Weapons Center
Sketches of various projectiles from Ordata
Special help by Richard Landgraff, Nathan Okun, Leo Fischer and William Jurens
For further information on these weapons, see USS Iowa Website
For a memorial to the men killed in Turret II, see USS Iowa Virtual Memorial
For information about the Mark 38 GFCS, see William E. Genereux Website
For a webpage devoted to a gun from USS New Jersey (BB-62), see Alan Zirkle Website
See Gene Slover's Navy Pages for on-line copies of BuOrd OP 769 "16-Inch Three Gun Turrets BB-61 Class" and OP 1091 "A.A. Range Table for 16-inch 50-caliber Gun"
Videos at USS Missouri BB-63 Website
11 December 2008 - Benchmark
20 July 2009 - Added Ordata as a source, added pictures of Mark 144, Mark 145 and comparison of AP Mark 8 and HC Mark 13
22 November 2009 - Corrected typographical error
06 August 2014 - Added armor thickness and details on 1980s reactivations
22 September 2014 - Minor additions to captions
10 January 2015 - Minor changes
15 May 2015 - Replaced photograph of USS Montana model with artist's conception drawing
30 May 2015 - Redid photograph of USS Iowa and added additional information on projectile stowage
08 July 2015 - Clarified note regarding rear bourrelets
22 November 2015 - Added Firing Cycle Operation
30 May 2016 - Converted to HTML 5 format
17 October 2016 - Added information and photographs of EX-148 projectile and propellant problems.
12 May 2017 - Added information about propellants for Target rounds
22 October 2017 - Added information about 1980s propellants and Accuracy in World War II
19 January 2018 - Reorganized notes
16 December 2018 - Added turret sketch, added to note regarding turret design problem, minor formatting changes
26 April 2019 - Added projectile storage information, sectional view and overhead views of turret, electric deck, projectile rings and powder handling room
29 May 2019 - Corrected typographical error