These were the first USN 8" (20.3 cm) guns to use separate rather than bag ammunition. With automatic shell handling and loading, a fire rate three times greater than that of previous 8" (20.3 cm) guns and coupled together with the use of "super-heavy" AP projectiles, these weapons made the Des Moines (CA-134) class the most powerful heavy cruisers ever built. One of the few large-caliber automatic gun designs that proved reliable in actual service use, these weapons were still giving good performance during the Vietnam War, some twenty-five years after they first entered service. Unfortunately, all this performance came at a steep price in weight, with the turrets mountings for these guns weighing 50% more than those in the previous Baltimore class.

During a fire mission off Vietnam in October 1972, USS Newport News (CA-148) suffered a premature projectile explosion in the center gun of Turret II that killed twenty crewmen. The projectile explosion was caused by a faulty auxiliary detonating fuze and this ignited a further nine cartridges in the ammunition hoists. The explosion caused extensive damage to the mounting and split the forward slide structure. Up until about six months prior to the explosion there had been a complete spare gun assembly in the supply system, but it had then been scraped because the Navy felt that it cost too much to let it sit in a warehouse. It was proposed to replace the damaged mounting with one taken from her decommissioned sisters, but this was rejected as being too expensive. As a result, the damage was not repaired and the turret was simply closed off.

These weapons were apparently the first loose-liner guns in service in the USN. Mark 16 Mod 0 was constructed of a monobloc autofretted barrel with a chrome-plated loose-liner held by a liner-locking ring. The barrel screwed into the housing which contained the breech block. Used a wedge-type vertical sliding breech block in place of the conventional interrupted screw. Unlike previous US 8" (20.3 cm) guns, these guns could load at any angle. An air bottle supplied pneumatic power to open and close the sliding breech block system used in these ships.

There was a Mark 16 Mod 1 bag gun. It is not clear if any of these were ever built.

Designation	8"/55RF (20.3 cm) Mark 16
Ship Class Used On	Des Moines (CA-134) class
Date Of Design	1943
Date In Service	1948
Gun Weight	17.14 tons (17.4 mt) 1
Gun Length oa	about 449.0 in (11.405 m) 2
Bore Length	440.1 in (11.179 m)
Rifling Length	383.5 in (9.741 m)
Grooves	(64) 0.070 in (1.78 mm) deep
Lands	N/A
Twist	Uniform RH 1 in 25
Chamber Volume	3,367 in3 (55.2 dm3)
Rate Of Fire	10 rounds per minute 3

• ^The weight including the slide was much greater than indicated above, as the oscillating weight per gun was 51.6 tons (52.4 mt) compared with 29.0 tons (29.5 mt) for the Mark 12 and Mark 15.
• ^The overall length from the muzzle to the rammer at the rear of the slide was 588.5 in (14.948 m).
• ^BuOrd was particularly - and justifiably - proud of this design. The high ROF figure was routinely and reliably achieved by all three ships of this class. Commented BuShips engineer E.A. Wright after viewing a demonstration bombardment by USS Newport News on 07 September 1949: "The automatic ammunition supply and loading worked perfectly and at the designed rate, which still seems to me phenomenal for that caliber."

Type	Separate
Projectile Types and Weights 1a 2a 3a	AP Mark 21 Mods 1 to 5 (super heavy) - 335 lbs. (152 kg) HC Mark 24 Mods 1 to 5 - 260 lbs. (118 kg) HC Mark 25 Mod 1 - 260 lbs. (118 kg)
Bursting Charge	AP Mark 21 - 5.03 lbs. (2.3 kg) Explosive D HC Mark 24 - 21.34 lbs. (9.7 kg) Explosive D HC Mark 25 - 21.37 lbs. (9.7 kg) Explosive D
Projectile Length	AP Mark 19 - 36.0 in (91.4 cm) HC Mark 24 - 34.56 in (87.8 cm) HC Mark 25 - 34.61 in (87.9 cm)
Cartridge Case Type, Size and Empty Weight 4a	Mark 1 - Brass, 203 x 1,277 mm, 57.0 lbs. (25.9 kg) Mark 2 - Brass, 203 x 789 mm, N/A
Propellant Charge	Full Charge - 77 lbs (34.9 kg) SPD or SPDN Full Flashless Charge - 82 lbs. (37.2 kg) SPCG Reduced Charge - 45 lbs. (20.4 kg) SPDN Reduced Flashless Charge - 46 lbs. (20.9 kg) SPDF
Muzzle Velocity	Full Charge - New Gun    AP - 2,500 fps (762 mps)    HC - 2,700 fps (823 mps) Reduced Charge - New Gun    AP - 2,000 fps (610 mps)    HC - 2,220 fps (677 mps)
Working Pressure	18.2 tons/in2 (2,870 kg/cm2)
Approximate Barrel Life	780 rounds
Magazine capacity per gun	150 rounds

• ^Other than the Des Moines (CA-134) class, AP Mark 21 (super heavy) was apparently issued only to the Baltimore (CA-68) and Oregon City (CA-122) classes. SP Common had a thin cap and a windscreen. HC Mark 25 was designed such that it could be forged from the base end.
• ^HC projectile bodies could be used with Point Detonating (PD) or Mechanical Time (MT) fuzes. When used with PD fuzes, they were considered to be HC rounds. When used with MT fuzes, they were considered to be AAC rounds. Automatic MT fuze setting was performed just before the shells were rammed, thus ensuring the minimum possible dead time.
• ^Radius of ogive for both AP and HC rounds was 83 inches (211 cm) or about 10crh. Bourrelet diameter was 7.977 inches (20.3 cm).
• ^Mark 1 cartridge case was for full charges while the Mark 2 was a short case for reduced charges.
• Unlike other USN semi-fixed ammunition, the cork plug sealing the cartridge case for this weapon was mounted flush with the end of the cartridge. The mouth of the cartridge was "cone crimped" or necked down to about the same diameter as the base of the projectiles. This heavy cone crimp allowed the weight of the projectile to be carried by the case itself rather than by the plug as they were rammed into the breech.

Range	Side Armor	Deck Armor
10,800 yards (9,880 m)	10.0" (254 mm)	---
15,400 yards (14,080 m)	8.0" (203 mm)	---
18,400 yards (16,820 m)	---	2.0" (51 mm)
20,800 yards (19,020 m)	6.0" (152 mm)	---
23,800 yards (21,760 m)	---	3.0" (76 mm)
24,400 yards (22,310 m)	5.0" (127 mm)	---
27,600 yards (25,240 m)	---	4.0" (102 mm)
28,600 yards (26,150 m)	4.0" (102 mm)	---

• These figures are taken from armor penetration curves issued in 1942 as shown in "US Naval Weapons."

Designation	Three-gun Turrets    Des Moines (3)
Weight	451 tons (458 mt)
Elevation	-5 / +41 degrees
Elevation Rate	8.2 degrees per second
Train	+150 / -150 degrees
Train Rate	5 degrees per second
Gun recoil	28 in (71 cm) 1c
Loading angle	Any angle

• ^This is the nominal figure. The maximum, metal-to-metal recoil length was 29 in (73.7 cm).
• The barbette design for these ships was cylindrical, not cone-shaped as in the previous Baltimore, Oregon City and Wichita classes.
• From "Naval Weapons of World War Two" by John Campbell: "Shells were stowed in the rotating structure on inner and outer live rings, both on two deck levels. The wing pusher hoists began between the inner and outer shell rings, while the center one was inside the inner ring starting on the axis. The shells were delivered to trays attached to arms pivoted on the cradle trunnions and thence to transfer trays which moved into position for ramming. The cartridges were similarly raised by three hoists from a deck level below the shells to pivoted trays and placed behind the shells. Shell and cartridge case were rammed together. After firing, the empty case was extracted and ejected by a chute running forward under the guns."
• This was the only major USN turret design where the guns were elevated by arc and pinion rather than the usual elevating screw and oscillating bearing. It was also the only major USN turret without an optical rangefinder, with two radars on each turret being used in their place.
• This mounting used a 125 hp training motor and each gun was elevated by a 25 hp motor. The rammers were powered by three 35 hp motors, the shell hoists by three 20 hp motors, the cartridge hoists by three 15 hp motors and each of the four live rings used a 20 hp motors. All of these motors drove hydraulic gear.
• The gun axes were 85 in (216 cm) apart.
• Each mounting requires a crew of about 44 to operate, a reduction of about 33 percent from earlier mountings.

"Naval Weapons of World War Two" by John Campbell
"US Naval Weapons", "US Cruisers: An Illustrated Design History" and "The Naval Institute Guide to World Naval Weapon Systems 1991/92" all by Norman Friedman
"U.S. Navy Bureau of Ordnance in World War II" by Lt. Cmdr. Buford Rowland, USNR, and Lt. William B. Boyd, USNR
"Cruisers of World War Two" by M.J. Whitley
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"U.S. Explosive Ordnance: Ordnance Pamphlet 1664 - May 1947" by Department of the Navy
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Turret II Explosion Report from USS Newport News (CA-148) Website
OP-1180, 8-Inch 3-Gun Turrets Main Armament For USS Salem Class, Turret Description And Operation, July 1947" at Historic Naval Ships Association
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Special help from Leo Fischer

07 February 2008 - Benchmark
27 January 2011 - Corrected typographical error
13 June 2016 - Converted to HTML 5 format
30 September 2018 - Reorganized notes
24 December 2018 - Added turret sketch
27 November 2021 - Updated OP-1180 and Turret II Explosion links to point to Wayback Archive