Intended for a new class of heavy cruisers during World War II which never made it beyond the sketch design stage.

The Mark IX* was to the older design standards, being of built-up construction with an A tube, jacket, breech ring and breech bush and would have been about the same weight as the 8"/50 (20.3 cm) Mark VIII. It would also have used the same breech as the Mark VIII with slight modifications. On relining with a tapered inner A tube, it was to have become the Mark IX. One gun was ordered from Vickers-Armstrong in April of 1941.

This prototype was abandoned when new design guidelines were adopted. Under the new rules, which were based upon Vickers-Armstrong's practice, stresses up to 24/27 of the yield point were now allowed rather than the prior standard of 20/27 of the yield point.

The Mark X* was designed to the new rules and would have had similar components as the Mark IX* but was now of lighter construction and had a new breech mechanism. This gun would have been designated as the Mark X after being relined with a tapered inner A tube. None of these guns were ever built and the order was cancelled in October 1942 along with the cruisers that would have carried them.

Gun Characteristics

Designation 8"/50 (20.3 cm) Marks IX and X
Ship Class Used On Proposed cruisers of World War II
Date Of Design 1941
Date In Service None built
Gun Weight Mark IX: 17.04 tons (17.3 mt)
Mark X: 12.5 tons (12.7 mt)
Gun Length oa 413.25 in (10.497 m)
Bore Length 400.0 in (10.160 m)
Rifling Length 346.3 in (8.796 m)
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume 4,300 in3 (70.46 dm3)
Rate Of Fire about 3 - 4 rounds per minute


Type Bag
Projectile Types and Weights SAPC 1: 290 lbs. (131.5 kg)
HE: 256 lbs. (116.1 kg)
Bursting Charge SAPC: 11.5 lbs. (5.2 kg)
HE: about 23 lbs. (10 kg)
Projectile Length SAPC: 36 in (91.4 cm)
Propellant Charge 72.25 lbs. (32.77 kg) SC 205
Muzzle Velocity 2,670 fps (814 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
  • ^The SAPC rounds were to a new longer and heavier design than those for the earlier Mark VIII guns.


Range with 290 lbs. (131.5 kg) SAPC
Elevation Muzzle Velocity Distance Flight Time
5.2 degrees 2,600 fps (792.5 mps) 10,000 yards (9,140 m) 14.3 seconds
9.9 degrees 15,000 yards (13,720 m) 24.4 seconds
16.3 degrees 20,000 yards (18,290 m) 37.1 seconds
25.4 degrees 25,000 yards (22,860 m) 53.6 seconds
43.9 degrees 30,000 yards (27,430 m) 81.9 seconds
45.0 degrees - 31,300 yards (28,620 m) -

Mount/Turret Data

  • Three-gun Turrets
    • All designs (3): N/A (probably Mark III)
Weight N/A
Elevation -3 / +45 degrees
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate N/A
Gun recoil N/A
Loading Angle N/A


Data from:

  • "Naval Weapons of World War Two" by John Campbell
  • "British Cruisers of World War Two" by Alan Raven and John Roberts

Page History

06 November 2006
18 February 2009
Added additional construction details