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.
|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)|
|Chamber Volume||4,300 in3 (70.46 dm3)|
|Rate Of Fire||about 3 - 4 rounds per minute|
|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)|
|Approximate Barrel Life||N/A|
|Ammunition stowage per gun||N/A|
|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)||-|