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, while the mountings differed 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. Guns and mountings were modernized and improved to correct problems regarding guns being in a single cradle and the complex loading system which was highly mechanized.
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").
| 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 |
| Type | Bag |
|---|---|
| Projectile Types and Weights 1 | SAP (1924): 276.2 lbs. (125.3 kg)
SAP (later issue): 261.2 lbs. (118.5 kg) HE: 243.77 lbs. (110.57 kg) |
| Bursting Charge | SAP (1924): 6.96 lbs. (3.157 kg)
SAP (later issue): 7.5 lbs. (3.4 kg) HE: 16.5 lbs. (7.5 kg) |
| Projectile Length | SAP (1924): N/A
SAP (later issue): 33.36 in (84.7 cm) Others: N/A |
| Propellant Charge | 92.2 lbs. (41.8 kg) 2 |
| Muzzle Velocity | SAP: 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 | 100 rounds 3 |
| Elevation | 276.2 lbs. (125.3 kg) SAP | 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 SAP 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 originally planned MV was 3,051 fps (930 mps) giving a range of 33,407 yards (30,547 m).
| Range | Angle of Obliquity (Degrees) 2a | ||||
|---|---|---|---|---|---|
| 90 | 80 | 70 | 60 | 50 | |
| 22,000 m (24,060 yards) | * | * | * | * | * |
| 20,000 m (21,870 yards) | 100 mm (3.93 in) | * | * | * | * |
| 18,000 m (19,690 yards) | 117 mm (4.61 in) | 115 mm (4.53 in) | 107 mm (4.21 in) | * | * |
| 16,000 m (17,500 yards) | 137 mm (5.39 in) | 135 mm (5.31 in) | 127 mm (5.00 in) | 112 mm (4.41 in) | * |
* = Does not penetrate the minimum thicknesses [100 mm (3.9 in)].
| Range | Angle of Obliquity (Degrees) 2a | ||||
|---|---|---|---|---|---|
| 90 | 80 | 70 | 60 | 50 | |
| 22,000 m (24,060 yards) | 96 mm (3.78 in) | 94 mm (3.70 in) | 88 mm (3.46 in) | 79 mm (3.11 in) | ** |
| 20,000 m (21,870 yards) | 109 mm (4.29 in) | 107 mm (4.21 in) | 100 mm (3.94 in) | 89 mm (3.50 in) | 74 mm (2.91 in) |
| 18,000 m (19,690 yards) | 127 mm (5.00 in) | 123 mm (4.84 in) | 116 mm (4.57 in) | 100 mm (3.94 in) | 87 mm (3.43 in) |
| 16,000 m (17,500 yards) | 150 mm (5.91 in) | 146 mm (5.75 in) | 137 mm (5.39 in) | 121 mm (4.76 in) | 102 mm (4.02 in) |
** = Does not penetrate the minimum thicknesses (minimum thickness not specified).
Maximum Ranges at which given Thicknesses of Horizontal Armor (Homogeneous) can be Penetrated
X1 = Penetration @ maximum range of opening of fire under conditions of exceptional visibility.
X2 = Penetration @ maximum range of opening of fire under conditions of normal visibility.
X3 = Penetration @ typical combat range band, once engaged.
| X Number | Range | Armor Penetration |
|---|---|---|
| X1 | 22,000 m (24,060 yards) | 43 mm (1.69 in) |
| X2 | 20,000 m (21,870 yards) | 91 mm (1.54 in) |
| X3 | 16 - 18,000 m (17,500 - 19,690 yards) | 25 - 31 mm (0.98 - 1.22 in) |
Data in this table taken from a memorandum of 10 December 1939 by the Commissione Permanente per gli Esperimenti del Materiale di Guerra (Mariperman) [Permanent Commission for the Experiments of the Material of War (Mariperman)].
| 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 for each gun. 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.
- The gun axes were about 35 inches (90 cm) apart for all mounting types.
"Italian Heavy Cruisers: From Tento to Bolzano" by Maurizio Brescia and Augusto de Toro
"Naval Weapons of World War Two" by John Campbell
"Questioni Di Tiro: E Altre le Artiglierie Navali Italiane Nella Guerra Nel Mediterraneo"
[Questions of Fire: And Others for the Italian Naval Artillery in the War in the Mediterranean] by Giuliano Colliva
"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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Memorandum of the Commissione Permanente per gli Esperimenti del Materiale di Guerra (Mariperman)
[Permanent Commission for Experiments of War Material (Mariperman)], 111/RP of 10 December 1939, "Dati circa gli effetti dei proietti su
bersaglio navale", diretto a Maristat [Data on the Effects of Projectiles on Naval Targets, addressed to Maristat]. Archive of the
Historical Office of the Navy [AUSMM], Artillery and Munitions Inspectorate fund [IAM], box 2, file 3, pages 7 and 8.
"Direttive e norme per l'impiego della Squadra Navale" [Directives and regulations for the use of the Navy]
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Press releases: Marina Militare
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Special help by Byron Angel
29 December 2007 - Benchmark
09 February 2021 - Converted to HTML 5 format, added mounting photograph, reorganized notes
19 March 2021 - Added note regarding gun spacing
18 January 2022 - Updated to latest format
07 January 2025 - Added data on mountings
15 August 2025 - Added Vertical and Horizontal Armor Penetration sections