United States of America
16"/45 (40.6 cm) Mark 6
Updated 24 August 2014

An improved weapon when compared to the older 16"/45 (40.6 cm) gun used on the Colorado class battleships, this weapon was a simpler, lighter design.  A major difference was that the mountings for these guns were specifically designed to handle the 2,700 lbs. (1,224.7 kg) AP Mark 8 projectile.  This gun had a slight advantage over the 16"/50 (40.6 cm) Mark 7 in terms of deck armor penetration due to its lower muzzle velocity.

During the Battle off Casablanca in November 1942, USS Massachusetts (BB-59) put two AP rounds through deck armor of the French battleship Jean Bart and temporarily silenced her only operational main battery turret with another AP round.  During the Battle of Guadalcanal in the same month, USS Washington (BB-56) sank the small Japanese battleship Kirishima with at least nine direct AP hits.

Constructed of liner, A tube, jacket, three hoops, two locking rings, liner-locking ring, yoke ring and screw box liner.  Some components were autofretted.  Used a Welin breech block which opened downwards.  As typical of USN weapons, the bore was chromium plated.  Mod 1 was similar except that there were tapped holes in the breech end for securing the hinge lug to the gun.  Mod 2 had a set of adapter sleeves to allow it to be used for regunning the Colorado class, but it is doubtful if any of these guns were actually in service aboard those ships.  About 120 guns of all mods were manufactured, with most being Mod 1.

One gun formerly used on USS South Dakota (BB-57) was converted to a 24" (60.96 cm) test gun by removing the liner, cutting the overall barrel length down to 492 inches (12.5 m) and then boring out the inside diameter to 24 inches (60.96 cm).  The finished gun was part of the Atlas missile development program and was used to fire 5,000 lbs. (2,268 kg) projectiles at a muzzle velocity of 1,300 fps (396 mps) or 100 lbs. (45.4 kg) projectiles at a muzzle velocity of  3,600 fps (1,097 mps).

WNUS_16-45_mk6_North_Carolina_guns_pic.jpg

Bow turrets of USS North Carolina BB-55
Note CXAM-1 radar above the main battery director, which dates this photograph as being sometime shortly after 27 August 1941
U.S. Naval Historical Center Photograph # 80-G-K-13971

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Click here for additional pictures
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Gun Characteristics
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Designation 16"/45 (40.6 cm) Mark 6
Ship Class Used On North Carolina (BB-55) and South Dakota (BB-57) classes
Date Of Design 1936
Date In Service 1941
Gun Weight 192,310 lbs. (97,231 kg) (without breech)
Gun Length oa 736.0 in (18.694 m)
Bore Length 720.0 in (18.288 m)
Rifling Length 616.9 in (15.668 m)
Grooves 96
Lands N/A
Twist Twist varied in individual guns of Mod 0, with some having a uniform RH 1 in 25 and others having a twist of increasing RH 1 in 50 to 1 in 32 at the muzzle.  Mod 1 and Mod 2 guns were all uniform RH 1 in 25 twist.
Chamber Volume 23,195 in3 (380.1 dm3)
Rate Of Fire 2 rounds per minute
Notes:

1) 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.

2) The bore was chromium plated for a distance of 625 inches (15.875 m) from the muzzle.

3) At 0704 local time on 8 November 1942, USS Massachusetts (BB-59) fired the first US 16 inch (40.6 cm) warshot of World War II.  In sixteen minutes she fired nine main battery salvos, scoring five hits on the incomplete French battleship Jean Bart.  Heavily damaged, Jean Bart was silenced for the rest of the day.  In addition, Massachusetts during this exchange sank a destroyer, four freighters and a floating dry-dock.  Between 1000 and 1030 on the same day, Massachusetts sank the French destroyer (contre-torpilleur) Boulonnais and shared in the sinking of the French destroyer Fougueux.  She fired 59.2% of her outfit in four hours of fighting (0704 to 1104) and then fired an additional 8% during the rest of the day.  During the entire action off Casablanca, USS Massachusetts in 134 salvos fired a total of 786 rounds out of a possible 800, an output of 98%.  During this engagement, she reported that most salvos had a dispersion of about 2 mils in deflection and about 200 to 300 yards (183 to 274 m) in range.  All of these were AP projectiles, as the ship had not yet received any HC projectiles.

4) During her battle with the Japanese battleship Kirishima, USS Washington (BB-56) opened fire at a gun range of 18,500 yards (16,900 m) using radar ranges and optical train and hits were definitely obtained by the third salvo.  In the first part of the battle, Washington fired 42 rounds in approximately 3 minutes (precise time not available) or 1.56 rpmpg.  During the second phase Washington fired 75 rounds in 5 minutes 24 seconds, or 1.54 rpmpg.  Washington fired a total of 117 out of a possible 131 shells, or 89%.  Of the 14 missed salvos, the most notable was the center gun of turret 3 which missed five salvos due to a ball check valve being jarred loose by the the firing shock, causing a loss of hydraulic pressure for that gun.  This loss of pressure prevented the pointer from matching up in the load position.  One other gun had a misfire which caused it to miss two salvos.  The other failures were primarily "error in drill" related.

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Ammunition
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Type Bag
Projectile Types and Weights AP Mark 8 Mods 0 to 8 - 2,700 lbs. (1,225 kg)
HC Mark 13 Mods 0 to 6 - 1,900 lbs. (862 kg)
HC Mark 14 Mod 0 - 1,900 lbs. (862 kg)
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)
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)
Propellant Charge Full Charge - 535 lbs. (242.7 kg) SPD

Reduced Charge - 295 lbs. (133.8 kg) SPD or SPDN
Reduced Charge Flashless - 315 lbs. (142.9 kg) SPCG

Muzzle Velocity Full Charge - New Gun
   AP - 2,300 fps (701 mps)
   HC - 2,635 fps (803 mps)

Full Charge - Average Gun
   AP - N/A
   HC - 2,525 fps (770 mps)

Reduced Charge - New Gun
   AP - 1,800 fps (549 mps)
   HC - 2,075 fps (632 mps)

Working Pressure 18.0 tons/in2 (2,835 kg/cm2)
Approximate Barrel Life
(see Note 4)
395 rounds
Ammunition stowage per gun 130 rounds
Notes:

1) For projectile data on the AP Mark 8, the HC Mark 13 and the HC Mark 14, see the 16"/50 (40.6 cm) Mark 7 data page.

2) The propellant was in six bags for both full and reduced charges.  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.

3) 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) to bring underweight projectiles up to weight.  Dye colors were assigned as follows in 1945:

   USS North Carolina - Green
   USS Washington - Orange
   USS South Dakota - Blue
   USS Indiana - Red
   USS Massachusetts - Green
   USS Alabama - No Dye

4) HC rounds at 2,525 fps (770 mps) were 0.74 ESR and at 2,000 fps (610 mps) were 0.09 ESR.  The Target rounds at 1,800 fps (549 mps) were 0.08 ESR, but it is noted that this gun could fire 2,860 Target rounds before exceeding liner life.

5) Bourrelet diameter was 15.977 inches (40.06 cm).

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Range
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Elevation
With 2,700 lbs. (1,224.7 kg) AP Mark 8
With 1,900 lbs. (861.8 kg) HC Mark 13
10 degrees
15,900 yards (14,539 m)
17,700 yards (16,185 m)
15 degrees
21,000 yards (19,202 m)
23,400 yards (21,397 m)
20 degrees
25,500 yards (23,317 m)
27,950 yards (25,568 m)
25 degrees
29,500 yards (26,975 m)
31,700 yards (28,986 m)
30 degrees
32,200 yards (29,444 m)
34,900 yards (31,913 m)
35 degrees
34,500 yards (31,547 m)
37,400 yards (34,219 m)
40 degrees
36,100 yards (33,010 m)
39,200 yards (35,844 m)
45 degrees
36,900 yards (33,741 m)
40,180 yards (36,741 m)
Notes:

1) Time of flight for AP Shell with MV = 2,300 fps (701 mps)
   10,000 yards (9,140 m): 14.5 seconds
   20,000 yards (18,290 m):  32.6 seconds
   30,000 yards (27,430 m):  56.6 seconds
   36,000 yards (32,920 m):  79.8 seconds

2) Range with the originally planned 2,240 lbs. (1,016 kg) AP Mark 5 was 40,200 yards (36,760 m) at a muzzle velocity of 2,520 fps (768 mps).

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Armor Penetration 2,700 lbs. (1,224.7 kg) AP Mark 8 Shell
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Range
Side Armor
Deck Armor
Striking Velocity
Angle of fall
0 yards (0 m)
29.74" (755 mm)
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2,300 fps (701 mps)
0.0
5,000 yards (4,572 m)
26.60" (676 mm)
0.76" (19 mm)
2,090 fps (637 mps)
3.0
10,000 yards (9,144 m)
23.51" (597 mm)
1.87" (28 mm)
1,900 fps (579 mps)
6.8
15,000 yards (13,716 m)
20.47" (520 mm)
3.04" (77 mm)
1,743 fps (529 mps)
11.7
20,000 yards (18,288 m)
17.62" (448 mm)
4.29" (109 mm)
1,604 fps (489 mps)
17.9
25,000 yards (22,860 m)
15.05" (382 mm)
5.76" (146 mm)
1,521 fps (463 mps)
25.4
30,000 yards (27,432 m)
12.77" (324 mm)
7.62" (194 mm)
1,490 fps (454 mps)
34.1
35,000 yards (32,004 m)
10.49" (266 mm)
10.57" (268 mm)
1,531 fps (488 mps)
45.2
Notes:

1) The above information is from "Battleships:  United States Battleships 1935-1992" for a muzzle velocity of 2,300 fps (701 mps) and is based upon the USN Empirical Formula for Armor Penetration.

2) Side Armor penetration with the originally planned AP Mark 5 was 29.68" (754 mm) at the muzzle, 16.24" (412 mm) at 20,000 yards (18,288 m) and 10.02" (210 mm) at 35,000 yards (32,004 m).  Information is from "Battleships:  United States Battleships 1935-1992" for a muzzle velocity of 2,520 fps (768 mps).

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Mount/Turret Data
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Designation Three-gun Turrets
   North Carolina (3) and South Dakota (3)
Weight 1,403 - 1,437 tons (1,426 - 1,460 mt)
Elevation Turrets I and III:  -2 / +45 degrees
Turret II:  0 / +45 degrees
Rate of Elevation 12 degrees per second
Train -150 / +150 degrees
Rate of Train 4 degrees per second
Gun Recoil 48 in (1.219m)
Loading Angle +5 degrees
Notes:

1) This three-gun mounting had individually sleeved guns which were spaced further apart than in the previous 14" (35.6 cm) three-gun mounts.  They also used delay coils, which delayed the firing of the guns by about 0.060 seconds (60 milliseconds).  The firing order was left, right, center.  These changes gave this weapon considerably improved dispersion characteristics when compared with the older 14" (35.6 cm) triple and three-gun mounts.  Turrets were essentially the same between the two classes with the South Dakota (BB-57) class having slightly thicker armor protection on most surfaces.

2) 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 60 hp motor for shell hoist and a 75 hp motor for power hoist.  Each of the two shell rings used a 40 hp motor.

3) The gun axes were 117 in (297 cm) apart.

4) Gun crew was two officers and 170 crewmen per turret.

5) Armor thickness for the North Carolina class (BB-55) as given in "Battleships:  United States Battleships, 1935 - 1992" by W.H. Garzke, Jr. and R.O. Dulin, Jr.:
    Face:  16.0 in (40.6 cm) Class B armor over 2.5 in (6.4 cm) STS
    Sides:  9.8 in (24.9 cm) Class A armor over 0.75 in (1.9 cm) STS
    Rear:  11.8 in (30.0 cm) Class A armor over 0.75 in (1.9 cm) STS
    Roof:  7.0 in (17.8 cm) Class A armor over 0.75 in (1.9 cm) STS

Armor thickness for the South Dakota class (BB-55) as given in "Battleships:  United States Battleships, 1935 - 1992" by W.H. Garzke, Jr. and R.O. Dulin, Jr.:
    Face:  18.0 in (45.7 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 (30.05cm) 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

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Data from
"Naval Weapons of World War Two" by John Campbell
"US Naval Weapons" by Norman Friedman
"Battleships:  United States Battleships, 1935-1992" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
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"USS Massachusetts 1945 Gunnery Doctrine" a USN BuOrd Publication
"U.S. Explosive Ordnance:  Ordnance Pamphlet 1664 - May 1947" by Department of the Navy
"Operational Experience of Fast Battleships:  World War II, Korea and Vietnam" a U.S. Naval Historical Center Publication edited by John C. Reilly, Jr.
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"Alnavco Log" Volume 7 Number 3, September 1972, Letter to the Editor by R.L. Love
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Special help by Keith Allen, Brad Fischer, Leo Fischer, Nathan Okun and Ed Jackson
Page History

22 October 2008 - Benchmark
30 December 2009 - Fixed typographical error, added information on USS Massachusetts at Casablanca
24 August 2014 - Added turret armor note