Britain 12"/25 (30.5 cm) Marks I and II

Britain
12"/25 (30.5 cm) Marks I and II
Updated 30 January 2009

Early breech loaders using black powder for propellant. HMS Colossus was the first British battleship to have BL main guns, steel construction and steel armor all in one ship.

The design of these guns was faulty and one burst on trial in HMS Collingwood on 4 May 1886, even though she was firing 3/4 charges. The failure caused the "A" tube to break into pieces in front of the "B" coils. As a result, HMS Colossus was directed not to fire these guns during her maiden cruise and all of these guns were withdrawn from service to be casehooped. They were then designated as Mark I* and mounted in the "No Man's Land" and "Horse Sand" forts at Spithead. The ships were then rearmed with newer, stronger 12"/35 (30.5 cm) guns.

Constructed of steel "A" tube into which the breech-block screwed, a wrought iron breech piece, three "B" coils of which the first was medium carbon steel and the others made of mild steel, one wrought iron "C" coil and a wrought iron jacket. There were no coils over the last 8 feet (2.44 m) of "A" tube at the muzzle end. All of the wrought iron parts were machined from hammer-welded coils. Mark I was a trunnioned gun for use in coastal defense batteries while the Mark II had thrust collars for naval saddle mountings, otherwise the two marks were identical. A total of 5 Mark I and 11 Mark II guns were manufactured.

Actual bore length was 25.13 calibers.

HMS Collingwood in 1882 with 12"/35 (30.5 cm) Mark II guns. She was later rearmed with 12"/35 (30.5 cm) Mark Vw guns.
Note the open barbettes

Gun Characteristics .

Designation	12"/25 (30.5 cm) Marks I and II
Ship Class Used On	Mark II: Colossus, Conqueror and Collingwood
Date Of Design	about 1880
Date In Service	1885
Gun Weight	43.8 tons (44.5 mt) inc. breech
Gun Length oa	328.5 in (8.344 m)
Bore Length	301.6 in (7.660 m)
Rifling Length	N/A
Grooves	N/A
Lands	N/A
Twist	N/A
Chamber Volume	N/A
Rate Of Fire	0.3 - 0.5 rounds per minute

Ammunition .

Type	Bag
Projectile Types and Weights	AP - 714 lbs. (324 kg)
Bursting Charge	N/A
Projectile Length	N/A
Propellant Charge	295 lbs. (134 kg) P.Br. (Prismatic Brown - cocoa)
Muzzle Velocity	1,914 fps (583 mps)
Working Pressure	N/A
Approximate Barrel Life	N/A
Ammunition stowage per gun	N/A

Range .

Elevation	With 714 lbs. (324 kg) Projectile
Range @ 12.5 degrees	9,400 yards (8,600 m)

Armor Penetration with 714 lbs. (324 kg) Projectile .

Range	Vertical Iron Plate
1,000 yards (9,140 m)	20.6 in (52.3 cm)
Note: Data from "British Battleships: 1850 - 1950."

Mount / Turret Data .

Designation	Twin Turret Colossus (2), Conqueror (1) Twin Barbette Collingwood (2)
Weight	N/A
Elevation	about - 3 / +10 degrees
Rate of Elevation	N/A
Train (see Note 2)	Colossus: 0 / about 170 degrees Conqueror: -45 / +45 degrees Collingwood: -90 / +90 degrees
Rate of Train	N/A
Gun Recoil	N/A
Loading Angle	about 10 degrees
Notes: 1) The guns on the Colossus class could only be loaded when the turret was trained to 0 degrees. The breech end of the weapons were lowered below the deck level by a hydraulic ram and then the charges were rammed into the breech from a compartment outside of the rotating structure. 2) The Colossus class had their guns in an amidships citadel with the turrets staggered. This allowed them to fire across the beam, although it is not clear if blast effects limited their use in such a manner. They could also fire directly ahead but not directly astern. For the Conqueror class, owing to blast effects on the bridge, it was found to be inadvisable to fire these guns abaft the beam, so the arcs of fire were limited to the figures above.

Data from
"Warrior to Dreadnought: Warship Development 1860-1905" by D.K. Brown
"British Naval Guns 1880-1945 No 4" article by John Campbell in "Warship Volume V"
"The Big Gun: Battleship Main Armament 1860-1945" by Peter Hodges
"British Battleships: 1860 - 1950" by Oscar Parkes

Page History

19 October 2007 - Benchmark
30 January 2009 - Fixed minor typographical errors