1) The primer cartridge can be fired either electrically or by percussion.

2) The bore was chromium plated for a distance of 690 inches (17.526 m) from the muzzle.

3) Projectile travel was 689.67 in (17.518 m) (new gun).

Added during 1950s Deployments
   Nuclear Mark 23 - 1,900 lbs. (862 kg)

Added during 1980s - 1990s 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)

HE-CVT - 64 in (162.6 cm)
ICM - 64 in (162.6 cm)
HE-ET/PT - 64 in (162.6 cm)

Post World War II Full Charge - 659.6 lbs. (299.2 kg) SPD D839
Post World War II Reduced Charge - 325.0 lbs. (147.4 kg) SPD/N/CG D840

HC - 2,690 fps (820 mps) (new gun)
HC - 2,615 fps (797 mps) (average gun)
HC - 2,075 fps (632 mps) (reduced charge)

1) 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 shell 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 (see picture of the disassembled Mark 8 on the additional pictures page).  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.

2) 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 larger, 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.

3) 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 warhead may have simply 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 on the additional pictures page.

4) 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. ( 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.

5) 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.

HE-ER Mark 148 (Planned)
13 in (33 cm) extended-range (ER), sub-caliber projectile with sabot.  ET-fuzed with a payload of 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 1,100 lbs. (500 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).

HE-ER Mark ? (Planned)
Another sub-caliber projectile with sabot, this one 11 inches (28 cm) in diameter.  This project was also cancelled about FY91.  For more information on this projectile, please see the "additional pictures" link above.

6) All full-caliber projectiles have a bourellet diameter of 15.977 inches (40.058 cm).

7) 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

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

9) 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, Nitrated-Cellulose (NC) 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.  Following World War II, Smokeless Powder Diphenylamine (SPD), a cooler-burning propellant, was adopted in order to prolong barrel life to about the second value given above.  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).  Later developments during the 1980s deployment led to putting a polyurethane jacket over the powder bags, which reduced the wear still further.  This jacket is 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 can no longer be rated in terms of ESR, as it is no longer the limiting factor.  Instead, the liner life is now 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 is now rated at having a liner life of 1,500 FER.

10) There are conflicting accounts about the number of rounds that could be carried by the Iowa class.  The following 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.

   16-inch Projectiles:
      Turret I:  387
      Turret II:  456
      Turret III:  367
   Total: 1,210

   16-inch Powder Canisters (each canister contains three propellant bags):
   Mark 4 are Full Service, Mark 8 are Reduced Service
      Turret I:  843 Mark 4 or 989 Mark 8
      Turret II:  928 Mark 4 or 1,148 Mark 8
      Turret III:  743 Mark 4 or 874 Mark 8
   Totals: 2,514 Mark 4 or 3,011 Mark 8

As was typical of US designs, the higher position of Turret II allowed significantly more projectile stowage compared to the other mountings.  There was also stowage for 9 drill projectiles for each turret.  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.

11) 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.

1) 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).

2) 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.

3) 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

4) 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

5) 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.

6) 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).

1) 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).

2) 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 up to 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.

3) Time fuzes were probably set by hand on the loading tray.

1) 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.  When the plans for using that weapon fell apart due to miscommunications between design bureaus, a new, smaller mounting design using the much lighter 16"/50 (40.6 cm) Mark 7 was generated.  This mounting was no larger than 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 mountings for the never-built Montana BB-67 class would have been similar but with thicker armor protection.

2) 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 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 on the additional pictures page.

3) Each turret requires 94 men to operate.

4) 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 of the shell rings used a 40 hp motor.

5) These mountings used delay coils, which delayed the firing of the center gun 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.

6) 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.

7) 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 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.

8) These turrets cost about $1,400,000 each, not including the cost of the guns themselves.