Britain
24 cm/50 (9.45") Elswick Pattern 'E'
9.2"/51 (23.4 cm) Mark XII
Updated 10 March 2009
A weapon with an interesting history.  These were originally designed and the first three completed by Elswick as 24 cm/50 (9.45") Pattern 'E' guns.  These guns were to be used on the Norwegian coastal defense ships Bjöergvin and Nidaros which were then under construction by Armstrongs.  At the start of World War I, the ships were taken over by Britain and renamed HMS Glatton and HMS Gorgon.  The existing guns were then relined down to 9.2" (23.4 cm) in order to use standard ammunition and three additional guns were completed to this caliber.  The actual bore length after relining was 51.35 calibers.

These weapons were some of the longest ranged guns in the world in 1918, exceeded only by the 18" (45.7 cm) guns used on the monitors HMS General Wolfe and HMS Lord Clive.  A total of six of these 9.2" (23.4 cm) guns were made, but two were lost when HMS Glatton suffered a serious fire and was scuttled in Dover Harbour in order to prevent a magazine explosion.  HMS Gorgon was scrapped after the war and the remaining four guns were offered to the Army in 1922.  This offer was declined and the guns were scrapped in 1923, a decision that might have been regretted in 1940 when there was a great need for long range guns for the defense of Dover.

Construction was of a normal wire-wound type with tapered inner 'A' tube, an outer "A" tube, wire-winding, B-tube over the muzzle portion and a jacket over the rear portion.  Relining to 9.2" (23.4 cm) made them slightly stronger, which allowed a smaller chamber and thus higher gas pressures.  These guns used an Elswick 3-motion short-arm breech mechanism.  The last two guns differed in having a thicker 'A' tube and a thinner 'A' tube along the chase and were completed in 1921.

Nomenclature Notes:  The 9.2"/35 (23.4 cm) Mark XIII was an Army Railroad gun of World War I with about 23 guns being built.  Some saw service during World War II and new guns were planned at that time, but none were completed.  The 9.2"/45 (23.4 cm) Mark XIV was a Vickers gun intended for a cancelled Italian armored cruiser.  These were similar to Elswick Pattern "H" used in the Greek cruiser Averov, except that the wire-winding extended for half the barrel length rather than the entire length.  Four guns were built, three being used during World War I as Railroad guns and the other on the Vickers range.  The 9.2"/46.7 (23.4 cm) Mark XV was essentially an updated Mark X.  This was intended to be used in twin coastal defense mountings.  Some 36 guns were ordered and at least a few were proofed, but it appears that none saw service use.
WNBR_92-51_mk12_Gorgon_pic.jpg

HMS Gorgon in 1918
The 9.2"/51 (23.4 cm) guns are in the bow and stern mounts
Note the high mainmast and that it was in the path of the funnel gases
IWM (CPL) Photograph
WNBR_92-51_mk12_Gorgon_postwar_pic.jpg

Gorgon in early 1919
Gorgon remained in commission after the war to aid investigations into the loss of sister-ship Glatton
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Gun Characteristics
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Designation 9.2"/51 (23.4 cm) Mark XII
Ship Class Used On Glatton Class monitors
Date Of Design about 1913
Date In Service 1918
Gun Weight 31.25 tons (32 mt)
Gun Length oa 485.35 in (12.328 m)
Bore Length 472.44 in (12.000 m)
Rifling Length 403.0 in (10.236 m)
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume for 9.2" (23.4 cm) 8,600 in3 (140.8 dm3)
Rate Of Fire 2 rounds per minute
Note:  Cost of each 24 cm (9.45") gun was about £6,000.
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Ammunition
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Type Bag
Projectile Types and Weights
(see Note 2)		 APC 4crh - 380 lbs. (172.4 kg)
HE 4crh - 380 lbs. (172.4 kg)
HE 8crh - 391 lbs. (177.4 kg)
Bursting Charge APC - N/A
HE - 40 lbs. (18.1 kg)
Projectile Length APC - N/A
HE 4crh - 33.3 in (84.6 cm)
HE 8crh - N/A
Propellant Charge Standard:  128.5 lbs. (58.3 kg) MD37
Super:  152 lbs. (68.9 kg) MD45
Muzzle Velocity
HE 4crh with standard charges		 2,940 fps (896 mps)
Muzzle Velocity 
HE 8crh with super charges		 3,060 fps (933 mps)
Working Pressure N/A
Approximate Barrel Life see Note 1
Ammunition stowage per gun
(see Note 3)		 130 rounds
Notes:

1) "Big Gun Monitors" states that after firing 200 rounds, most with supercharges, "the guns were already half-worn [out] by October 1918."

2) The 8crh round may actually be a 5/10crh round.

3) At least six ready rounds were carried in the gunhouse.

4) The original 24 cm (9.45") projectile would have weighed 419 lbs. (190 kg).  Muzzle velocity was 2,900 fps (884 mps) using a 144 lbs. (65.3 kg) charge.  These projectiles were required to be able to penetrate 8.75 in (22.2 cm) of Krupp cemented (face hardened) armor at 7,650 yards (7,000 m).  CPC projectiles were to cost £15 each and the charges £11 each.
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Range
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Elevation With 380 lbs. (172.4 kg) HE 4crh Shell
40 degrees
Standard Charges		 about 30,000 yards (27,430 m)
Elevation With 391 lbs. (177.4 kg) HE 8crh Shell
40 degrees
Super Charges		 about 39,000 yards (35,660 m)
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Mount / Turret Data
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Designation Single Mounts
   Glatton (2):  Mark IX
Weight  194.2 tons (197.3 mt)
Elevation
(see Note 2)		 -5 / +40 degrees
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate N/A
Gun recoil N/A
Loading Angle N/A
Notes:

1) These turrets were hydraulically operated.  The ammunition hoist carried both projectile and cordite bags.  These were delivered to the left side of the gun.  The projectile was then moved onto a loading tray which swung around to the breech, in line with a hydraulic rammer.

2) Original maximum elevation as a 24 cm (9.45 inch) gun was +35 degrees.

3) Each turret cost £26,000.
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Data from
"Big Gun Monitors:  The History of the Design, Construction and Operation of the Royal Navy's Monitors" by Ian Buxton
"Technical Topics No 2:  Persistent Errors in Descriptions of Ships' Armament" article in "Warship Volume I" and "British Naval Guns 1880-1945 No 7" article in "Warship Volume VI" both by John Campbell
Page History

25 August 2006 - Benchmark
10 March 2009 - Added construction details, post-war picture of Gorgon, ammunition notes and turret elevation note