Description

More powerful than the previous 20.3 cm (8") Model 1924, these were probably Italy's best cruiser guns of World War II. The guns were the same for both Models, with the difference being that the M1927 mountings used on the Zara Class had thicker armor than the M1929 used on Bolzano.

These guns suffered from shell dispersion problems as they were mounted too close together. The muzzle velocity was lowered during trials in a largely unsuccessful attempt to reduced the dispersion. The guns were not individually sleeved.

Built with A tube, full length jacket, breech ring and a loose liner which could be replaced on-board ship. Used a Welin breech-block which was hydraulically operated.

Actual bore diameter was 20.32 cm (8.0").

Gun Characteristics

Designation 203 mm/53 (8") Model 1927 and Model 1929
Ship Class Used On Zara class: Model 1927
Bolzano: Model 1929
Date Of Design 1927
Date In Service 1931
Gun Weight 25 tons (27,216 kg)
Gun Length oa 440.0 in (11.177 m)
Bore Length 424.0 in (10.770 m)
Rifling Length 355.6 in (9.031 m)
Grooves 52
Lands N/A
Twist Uniform RH 1 in 30
Chamber Volume 4,831 in3 (79.16 dm3)
Rate Of Fire 2 - 3.8 rounds per minute

Ammunition

Type Bag
Projectile Types and Weights AP: 276.2 lbs. (125.3 kg)
HE: 243.77 lbs. (110.57 kg)
Bursting Charge AP: 7.5 lbs. (3.4 kg)
HE: 18.0 lbs. (8.2 kg)
Projectile Length AP: 33.36 in (84.7 cm)
HE: N/A
Propellant Charge 92.2 lbs. (41.8 kg) 1
Muzzle Velocity APC: 2,953 fps (900 mps)
HE: 3,084 fps (940 mps)
Working Pressure 20.6 tons/in2 (3,250 kg/cm2)
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
  1. ^Propellant was in two bags.

Range

Range with assorted shells
Elevation 276.2 lbs. (125.3 kg) APC 243.77 lbs. (110.57 kg) HE
45 degrees 34,521 yards (31,566 m) about 34,500 yards (31,550 m)

As originally designed, the MV for AP shells was 3,117 - 3,150 fps (950 - 960 mps) and the range was 37,410 yards (34,208 m). For the HE shells, the MV was 3,051 fps (930 mps) and the range was 33,407 yards (30,547 m).

Mount/Turret Data

Designation
  • Twin Turrets
    • Zara (4): Model 1927
    • Bolzano (4): Model 1929
Weight Model 1927: 178.1 tons (181.0 mt)
Model 1929: N/A, but lighter than Model 1927
Elevation -5 / +45 degrees
Elevation Rate 5 degrees per second
Train about +150 / -150 degrees
Train Rate 6 degrees per second
Gun recoil 21.7 in (55 cm)
Loading Angle Any angle

These mountings had two-stage propellant hoists and a single-stage projectile hoist. It appears that propellant bags were stored in protective containers from which they were removed just before loading.

Magazines were above the shell rooms.

Mountings used electric training and elevation. Rammers were hydraulically powered, although those on Pola may have been electrically powered.

Additional Pictures

Sources

Data from:

  • "Naval Weapons of World War Two" by John Campbell
  • "Italian Warships of World War II" by Aldo Fraccaroli
  • "Warship Pictorial #23: Italian Heavy Cruisers of World War II" by Gordon E. Hogg and Steve Wiper

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