Shipbucket

those were.... the cruiser-destroyer guns, right? that would make sense.

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No, these were Vickers designs.
The N1 began in 1948 as a twin or single 5in L/70 mount with a rate of fire of 66rpm. Vickers Barrow (189 tons) and Vickers Elswick (113 tons) designed twin turrets.
The N2 was a 1952 project and cancelled in September 1953 but still shows up on several of these cruiser projects until 1955.
A twin turret with 40rpm rate of fire, basically a smaller and lighter N1 but based on a land-based AA gun project. The turret would weigh 90-95 tons (55 tons for single barrel version), elevation 90 degrees. RoF only sustained for 1 minute and then 10rpm after to reduce barrel wear. 58lb shell, 3200fps muzzle velocity. Upper and lower feeds (lower somewhat like 3in Mk6 system) provided 20 shells each in the hopper and 20 more in the endless chain. AA fire would be 5-6 bursts each of 20sec with 10-15sec intervals. SU fire 100 rounds continuous in Mk2 mount. It would take 1.5-5 minutes to switch ammunition types in the feed system. Outfit was 500 shells per turret.

I've now updated the GW36 gun cruiser with the new mount, which I've drawn from sketchy sources available.

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Hate to say it Hood, but your GW36 drawing is still showing the 5.25's

@Hood " 528lb shell" ?? Typo I suppose. If not, I've got the gun design story somewhere .....

Those look like meaty turrets. They are twin 5"? Do I remember single/twin 5" on the Destroyer/Cruiser you did a while back?

Smurf I would not mind seeing a gun with a 528lb shell (10") for shore bombardment use.

Whoops! Yes a typo indeed, I've corrected it to 58lb.

It is a meaty turret, I scaled it off two separate drawings with a similar shaped outline for the turret but I make no claims to accuracy as I've never seen detailed pictures or plans (only a frontal view).
What killed the 5in twin on these cruisers was that it was expected to take eight years to fully develop, and as can be seen the twin 6in Mk.26 was not much smaller (although lighter) and closer to production.

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Was development of the 5" proposed to give commonality of ammunition so that ships of the UK could act with US Battle Groups and be part of the supply chain? Has this hurt UK development not having common weaponry?

Are we not talking about the 5"/70 http://www.navweaps.com/Weapons/WNBR_51-50_mk1.htm developed with (like 3"/70) rather than anything the USN actually used ?

Yes JSB, the N1-N2 series. Those are the guns Hood was saying would take 8 years to go through all the proving stages before entering service. Though if the guns could have been built in conjunction with the US then that time may have been shortened. Without a common gun type then the two navies need to use their own support equipment for any ships deployment.

GW50A May 1955

The Sea Lords on 28 January 1955 directed DNC to prepare a 5in armed cruiser based on GW36. The resulting GW39 inspired Staff Requirement TSD 2295/55 for a cruiser with two twin 5in, 48 missiles and 31kts deep and dirty. This became GW41. Further developments included the 6in Mk26 and a notional single 6in mount (GW42-46). These provided the Sea Lords with useful guidance but all were poor designs with inefficient use of magazine space. In April 1955 the Controller asked for another series of designs, by now Armstrong Whitworth had supplied more concrete data on the Sea Slug weight and dimensions and a decision was taken to abandon the 5in gun. However, the 5in still crops up, including the 4.5in Mk.6. GW48 was the smallest, GW49 had twin 5in guns, GW50 was a revised GW47 with three YEAD units to provide adequate speed, displacing 13,000 tons and dimensions of 570 x 76 x 19ft 6in.
When Mountbatten visited Bath on 17 May he was shown the sketch design of GW50A, basically GW50 with a displacement margin added. The design grew too. Displacement 13,500 tons (deep). Dimensions were 600ft (oa) (590 ft wl) x 76ft x 19ft 3in. Speed was 31.5kts deep and clean with three 35,000shp YEAD sets, endurance 4,500nm at 20kts. Armament was two twin 5in, four twin 40mm L/70 and 48 Sea Slug missiles. The radar fit was one Type 901 director, six MRD-3, Type 984, Type 992 and Type 974. A self-defence Type 176 sonar was likely too. Armour protection was 1.5in side and deck except for the machinery areas which had 1in deck.
Drawing Note: This drawing based on official sketch drawings of GW50A


GW51A May 1955

GW51 was the 6in armed version of GW50 with a raised bridge. Displacement was 13,900 tons; dimensions 590 x 77 x 19ft 6in and 31.75kts speed. When Mountbatten visited Bath on 17 May he was shown the sketch design of GW51A, basically GW51 with a displacement margin added. Displacement 14,500 tons (deep). Dimensions were 625ft (oa) (615 ft wl) x 77ft x 19ft 6in. Speed was 31.5kts deep and clean with three 35,000shp YEAD sets, endurance 4,500nm at 20kts. Armament was two twin 6in, four twin 40mm L/70 and 48 Sea Slug missiles. The radar fit was one Type 901 director, six MRD-3, Type 984, Type 992 and Type 974. A self-defence Type 176 sonar was likely too. Armour protection was 1.5in side and deck except for the machinery areas which had 1in deck. Complement was 78 officers and 970 ratings.
Drawing Note: This drawing based on official sketch drawings of GW51A


GW52A May 1955

GW52 was a version of GW51 with two twin 3in L/70 mounts aft, adding 160 tons of weight and 10ft to the length. Displacement was 14,500tons; dimensions 600 x 78 x 19ft 9in and 31.75kts speed. When Mountbatten visited Bath on 17 May he was shown the sketch design of GW52A, basically GW52 with a displacement margin added. Displacement 15,100tons (deep). Dimensions were 635ft (oa) (626ft wl) x 78ft x 19ft 9in. Speed was 31.5kts deep and clean with three 35,000shp YEAD sets, endurance 4,500nm at 20kts. Armament was two twin 6in, two twin 3in L/70, two twin 40mm L/70 and 48 Sea Slug missiles. The radar fit was one Type 901 director, six MRD-3, Type 984, Type 992 and Type 974. A self-defence Type 176 sonar was likely too. Armour protection was 1.5in side and deck except for the machinery areas which had 1in deck. Complement was 76 officers and 970 ratings.
Drawing Note: This drawing based on official sketch drawings of GW51A

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