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
