Description

Used on the only dreadnoughts purchased by Argentina, this gun was probably a copy of the USA 12"/50 (30.5 cm) Mark 7 with an additional breech weight.

Gun Characteristics

Designation 12"/50 (30.5 cm) Bethlehem
Ship Class Used On Rivadavia class
Date Of Design 1910
Date In Service 1914
Gun Weight 66 tons (67 mt)
Gun Length oa 607.25 in (15.424 m)
Bore Length 594 in (15.087 m)
Rifling Length 500.925 in (12.724 m)
Grooves (72) 0.075 in deep (1.90 mm)
Lands N/A
Twist Increasing RH 1 in 50 to 1 in 32
Chamber Volume 11,863 cu. in. (194.400 liters)
Rate Of Fire 2 - 3 rounds per minute

Data in this table is taken from the USA 12"/50 (30.5 cm) Mark 7 Mod 1.

Ammunition

Type Bag
Projectile Types and Weights
(see Note 1)
AP Mark 15: 870 lbs. (394.6 kg)
Bursting Charge AP Mark 15: 25.0 lbs. (11.3 kg) Explosive D
Projectile Length AP Mark 15: 42.0 in (106.7 cm)
Propellant Charge 337 lbs. (152.9 kg) NC 1
Muzzle Velocity
(see Note 4)
AP: 2,900 fps (884 mps)
Working Pressure 17.5 tons/in2 (2,760 kg/cm2)
Approximate Barrel Life 200 rounds
Ammunition stowage per gun 100 rounds

Data in this table is for the USA AP Mark 15.

Bourrelet diameter was 11.977 inches (30.4 cm).

1

The propellant was in four bags.

Range

870 lbs. (394.6 kg) AP Shell with a Muzzle Velocity of 2,900 fps (884 mps)
Elevation Distance Striking Velocity Angle of Fall Flight Time
0.3 degrees 1,000 yards (910 m) 2,802 fps (854 mps) 0.4 -
1.4 degrees 4,000 yards (3,660 m) 2,521 fps (768 mps) 1.6 4.4 seconds
10.3 degrees 19,000 yards (17,370 m) 1,524 fps (465 mps) 15.7 -
11.1 degrees 20,000 yards (18,290 m) 1,489 fps (454 mps) 17.3 30.1 seconds
12.8 degrees 22,000 yards (20,120 m) 1,432 fps (436 mps) 20.5 34.3 seconds
14.7 degrees 24,000 yards (21,950 m) 1,392 fps (424 mps) 23.9 38.7 seconds

Armor Penetration

Armor Penetration for 870 lb. (394.6 kg) AP Shell
Range Side Armor Deck Armor
6,000 yards (5,490 m) 17.4" (442 mm) ---
9,000 yards (8,230 m) 14.7" (373 mm) ---
12,000 yards (10,920 m) 12.3" (312 mm) ---

This data is from "Elements of US Naval Guns" of 1918. It is corrected for angle of fall.

Mount/Turret Data

Designation Two-gun Turrets: Rivadavia (6)
Weight 491 tons (498.86 mt)
Elevation -5 / +15 degrees
Elevation Rate N/A
Train
(see Note)
Bow and stern: about -150 / +150 degrees
Amidships: 100 degree arc 1
Train Rate N/A
Gun Recoil 38 in (96.5 cm)
Loading Angle Any angle
1

Amidships turrets were probably limited to an arc of about 90 degrees in order to minimize blast effects.

Pictures

Sources

Data from:

  • "Naval Weapons of World War Two" by John Campbell
  • "US Naval Weapons" and "US Battleships: An Illustrated Design History" both by Norman Friedman
  • "Battleships: United States Battleships, 1935-1992" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
  • "Battleships of World War I" by Peter Hore
  • "Battleships of World War Two: An International Encyclopedia" by M.J. Whitley

"Range and Ballistic Tables 1935" by U.S. Department of Ordnance and Gunnery

Page History

12 July 2008 - Benchmark

23 February 2010 - Added picture of Moreno gun

17 May 2011 - Added picture of Rivadavia