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) |
| 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) HE: N/A |
| 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.
| 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) | - |
Data from:
- "Naval Weapons of World War Two" by John Campbell
- "British Cruisers of World War Two" by Alan Raven and John Roberts
- 06 November 2006
- Benchmark
- 18 February 2009
- Added additional construction details