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").
|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)|
|Twist||Uniform RH 1 in 30|
|Chamber Volume||4,831 in3 (79.16 dm3)|
|Rate Of Fire||2 - 3.8 rounds per minute|
|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)
|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|
- ^Propellant was in two bags.
|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).
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.
- The gun axes were about 35 inches (90 cm) apart for all mounting types.
"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
Press releases: Marina Militare
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