6"/50 (15.2 cm) BL Mark XVII
6"/50 (15.2 cm) BL Mark XXI
Updated 15 March 2016

The Mark XVII was another 6" (15.2 cm) gun designed for the foreign markets, this one built by Elswick for the Chilean battleships Almirante Latorre and Almirante Cochrane.  The Almirante Latorre was almost completed in 1914 at the start of World War I and shortly thereafter she was taken over by the British and renamed HMS Canada.  The Almirante Cochrane lay half-completed until after the war when she was renamed HMS Eagle and converted to an aircraft carrier with these 6" (15.2 cm) guns being used as her main gun armament.  HMS Canada was resold to Chile in 1920 and remained in service as Almirante Latorre until decommissioned in 1958.  HMS Eagle was sunk by a German U-boat in 1942.

Of built-up construction and wire wound, generally similar to the Mark 12.  Used a hand-worked Welin breech-block and an Elswick sliding hinge mechanism, with the fore portion of the breech being conical.  A total of 29 guns were made.

The Mark XXI was originally ordered by Chile as a coastal defense gun and was almost identical to the Mark XVII except for a longer chamber, B tube and jacket rather than a full length jacket.  Sixteen guns were made of which ten were taken over by the British Army for coast defense.

The data that follows is for the Mark XVII except where specified.


HMS Eagle
The 6" (15.2 cm) guns are in the single mounts under the flight deck


6"/50 (15.2 cm) gun from Chilean battleship Latorre now at Museo de Cañones Navales in Bahia de Valparaíso, Chile
Photograph copyrighted by Carlos Mey and used here by his kind permission

Gun Characteristics
Designation 6"/50 (15.2 cm) BL Mark XVII
6"/50 (15.2 cm) BL Mark XXI
Ship Class Used On Mark XVII:  Canada and Eagle
Mark XXI:  Coast defense batteries
Date Of Design 1913
Date In Service 1914
Gun Weight 19,524 lbs. (8,856 kg)
Gun Length oa 310.4 in (7.885 m)
Bore Length 300.0 in (7.620 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume 1,650 in3 (27.04 dm3)
Rate Of Fire
(see Note)
5 - 7 rounds per minute
Note:  The Rate of Fire figure given above is found in references for British guns of this caliber, but "Warrior to Dreadnought:  Warship Development 1860-1905" quotes Jellicoe's 1906 figures for rates of fire for these guns in gunlayers' tests and in battle practice and notes that the latter figures corresponded well to those actually attained by the Japanese at Tsushima:

   Gunlayers Test:  12 rounds per minute
   Battle Practice:  4 rounds per minute

In "Jutland:  An Analysis of the Fighting" by John Campbell, it is stated that Canada's hoists were capable of supplying about 5.5 rounds per minute, a more rapid figure than her RN contemporaries.

Type Bag
Projectile Types and Weights CPC 4crh - 100 lbs. (45.3 kg)
HE 4crh - 100 lbs. (45.3 kg)
Bursting Charge CPC - 7.5 lbs. (3.4 kg)
HE - 13.3 lbs. (6.0 kg)
Projectile Length CPC - 23.5 in (59.7 cm)
HE - 22.9 in (58.2 cm)
Propellant Charge 28.6 lbs. (13.0 kg) MD26
28.1 lbs. (12.76 kg) SC140
Muzzle Velocity 2,905 fps (885 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun 200 rounds
Elevation With 100 lbs. (45.36) CPC Shell
Range @ 20 degrees 16,190 yards (14,800 m)
Mount / Turret Data
Designation Single Mounts
   Canada (16):  PXII
   Eagle (9):  PXII*
Weight 30,520 lbs. (13,844 kg) without shield
Elevation PXII:  -7 / +15 degrees
PXII*:  -7 / +20 degrees
Elevation Rate Manual operation, only
Train about +80 / -80 degrees
Train Rate Manual operation, only
Gun recoil N/A

1) HMS Canada had her two after guns removed in 1916 after it was found that blast from the 14-inch "Q" turret caused problems.

2) The shields for these guns were of a new Vickers design which allowed full elevation and depression over all arcs of fire.

Data from
"Warrior to Dreadnought:  Warship Development 1860-1905" by D.K. Brown
"British Battleships of World War One" by R.A. Burt
"Jutland:  An Analysis of the Fighting," "Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 12" article in "Warship Volume VIII" all by John Campbell
"British Cruisers of World War Two" by Alan Raven and John Roberts
"A Concentrated Effort:  Royal Navy Gunnery Exercises at the End of the Great War" article by William Schleihauf in "Warship International" No. 2, 1998
Page History

05 April 2008 - Benchmark
11 February 2012 - Updated to latest template
04 February 2014 - Added ammunition stowage and mounting note about gun shields.
15 March 2016 - Corrected sinking of HMS Eagle, miscellaneous additions