1/200 Royal Navy 6"/50 (15.2cm) BL MKXXI x4 (HMAS Sydney)
1/200 Scale Royal Navy 6"/50 (15.2cm) BL MKXXI x4 (HMAS Sydney). Highly detailed guns modelled from plans and many reference photographs. This is the set specifically for HMAS Sydney, with Footrail on X Turret and large Eyebolts on B Turret).
- 4x Turrets
- Highly detailed and accurate parts, modelled from plans and photographic reference of an actual surviving example at Devonport Naval Base, Auckland
- Details include: Rivets, Hex nuts, Armour Panel Lines, Sighting Port Hatches, Sighting Periscope, Vents, Crew Access Hatches and Ladders
- Barrels are printed separately and can be elevated as desired.
This weapon was developed as a result of the London Cruiser Conference of January 1929 which restricted cruiser gun size to 6” (15.2 cm). A reliable weapon, although somewhat obsolescent in its use of bag ammunition, manual ramming and manually-operated breech mechanism.
Like many contemporary mid-caliber designs, it was originally planned to use this gun in the AA role. However, again like many contemporary designs, the slow rates of train, elevation and firing made it ineffective in that role. For this reason, later designs dropped the high angle requirement, a decision which also reduced the mounting weights.
The early Southampton (“Town”) class cruisers experienced dispersion problems with spreads up to 700 yards (640 m) being recorded. It was thought that air currents set up by the wing shells were affecting the flight of the center projectile even though the center gun was set back to reduce the problems. However, a Professor Hay, who was in charge of the gunnery trials of HMS Newcastle at Shoeburyness in October 1937, theorized that as the cordite charge was much smaller than the chamber, that its burning caused more pressure at the top of the chamber than at the bottom and sides and thus produced an uneven vibration along the gun barrel. Special high speed cameras were mounted in the turret and these showed that some shells were indeed canted at the muzzle which increased the dispersion. As a result, a timing circuit was introduced which delayed the firing of the center gun, thus increasing the shell separation and reducing dispersion.
This gun consisted of an A tube, partial jacket, breech ring and breech bush screwed into the jacket and used a Welin breech-block with a hand-operated Asbury mechanism. If relined with a inner tapered A tube, the gun was then designated as Mark XXIII*. A total of 469 guns of all types were manufactured.
Consideration was given to using this weapon as a heavy field gun, but none were ever used in that role.
There was a proposed variation tentatively designated as the Mark XXIV which was for the quadruple mounting originally intended for HMS Edinburgh and HMS Belfast. This gun would have used a power-worked breech mechanism, but it was cancelled along with the quadruple mounting.
The Mark XXIV designation was ultimately given to an Army coastal defense gun having the same performance as the Mark VII*, but constructed with a loose barrel. About 140 of these were built during World War II.