Britian
6"/40 (15.2 cm) QF Marks I, II and III
Updated 29 August 2011
These guns were used on most pre-dreadnoughts and cruisers built between 1890 and 1905.  The Mark I and Mark II were only slightly different in construction and are normally listed together in armament lists.  Mark III was a trunnioned version of the Mark I.

Mark I was EOC Pattern "Z" and was of built up construction while Mark II was a Woolwich design.  The Mark III was known to EOC as "Z1."  All used a 3-motion breech mechanism but most were later converted to a single motion breech mechanism.  Guns so converted had a "B" added after the Mark number.  A total of 137 Mark I, 760 Mark II and 53 Mark III guns were made for Britain.  In addition, numerous 6" (15.2 cm) EOC guns of the same or similar designs were made for other countries, including Italy and Japan.

Some British guns were employed as AA weapons during World War I, but this did not prove very successful.  63 Mark II guns were transferred to the Army, where they were bored out and converted to 8" (20.3 cm) howitzers.

Nomenclature note:  The 6"/45 (15.2 cm) QF Mark IV designation was given to twelve guns purchased from the USA firm of Bethlehem Steel early in World War I.  Eight of these were used in coastal defenses at Scapa Flow and four were used on DAMS.  These guns may actually have been the Bethlehem 6"/44 (15.2 cm) Mark 9 or a close relation.
WNBR_3pounder_H_mk1_Furious_pic.jpg

HMS Furious in 1898
6"/40 (15.2 cm) gun in bow pedestal mount
U.S. Naval Historical Center Photograph # NH 61062
WNBR_6-40_mk1_Hermes_pic.jpg

6"/40 (15.2 cm) guns on HMS Hermes
The original postcard is titled "Captain Scott's Dotter" which was a mechanism used to teach gunsighting techniques
Photograph courtesy of Brian Cave and Paul Benyon
WNBR_6-40_mk1_breech_pic.jpg

6" (15.2 cm) gun on HMS Ariadne ca. 1903
Note the three motion breech and sailors holding rammer, projectile and propellant casings
Bain News Service Photograph
Library of Congress Photograph ID LC-DIG-ggbain-16785
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Notman Studio/Library and Archives Canada Photograph PA-028473
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Images at The Vickers Photographic Archive

See photograph 6487

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Gun Characteristics
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Designation 6"/40 (15.2 cm) QF Marks I, III and III
Ship Class Used On
(see Note)		 Pre-dreadnoughts
   Royal Sovereign, Hood, Renown, Majestic and Canopus classes

Armored cruisers
   Diadem, Powerful, Royal Arthur and Edgar classes

Small cruisers
   Blake, Aeolus, Brilliant, Iphigenia, Hermes, Challenger, Arrogant, Eclipse and Astraea classes

Rearmed Ships
   Trafalgar, Indefatigable, Intrepid, Rainbow and Sirius

Added to 
   Hercules, Immortalité and Narcissus

During World War I these guns were used on most large monitors and many AMCs and DAMS
 

These guns were used as secondaries on the Italian Garibaldi class armored cruisers, with the Argentine cruisers Pueyrredon and Admiral Belgrano using Mark II guns
Date Of Design 1888
Date In Service 1892
Gun Weight 6.6 tons (6.7 mt)
Gun Length oa 249.25 in (6.331 m)
Bore Length 240.0 in (6.096 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume 832 in3 (13.63 dm3)
Rate Of Fire 5 - 7 rounds per minute
Note:  Campbell in "British Naval Guns 1880-1945 No 11" says that these guns were used to rearm HMS Superb.  There is some evidence to support this in "British Battleships:  1860 - 1950" by Parkes, but this is contradicted by other information contained in that same work which says that Superb was rearmed with 6 inch (15.2 cm) BL guns.  As Superb was reftted between 1887 to 1891, this predates the introduction of the 6"/40 (15.2 cm) on the Royal Sovereign class.  For these reasons, I believe that Superb was actually rearmed with 6 inch (15.2 cm) BL guns.
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Ammunition
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Type Separate
Projectile Types and Weights CPC - 100 lbs. (45.3 kg)
HE - 100 lbs. (45.3 kg)
Bursting Charge N/A
Projectile Length 26.5 in (67.3 cm)
Propellant Charge 29.75 lbs. (13.49 kg) EXE
13.25 lbs. (6.01 kg) Cord 30
15.94 lbs. (7.23 kg) MD26
Muzzle Velocity EXE - 1,882 fps (574 mps)
Cord - 2,230 fps (670 mps)
MD - 2,243 fps (684 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
Note:  Projectiles were 2crh.
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Range
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Elevation With 100 lbs. (45.36) HE Shell
Range @ 15 degrees With Cord 30 - 10,000 yards (9,140 m)
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Mount / Turret Data
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Designation
(see Notes 1 and 2)		 Single Mounts:  CPI and PII

Pre-dreadnoughts
   Royal Sovereign (10), Hood (10), Renown (10), Majestic (12) and Canopus (12)

Armored cruisers
   Diadem (16), Powerful (12), Royal Arthur (12) and Edgar (10)

Small cruisers
   Blake (10), Aeolus (2), Brilliant (2), Iphigenia (2), Hermes (11), Challenger (11), Arrogant (2), Eclipse (2) and Astraea (2)

Rearmed Ships
   Trafalgar (6), Indefatigable (2), Intrepid (2), Rainbow (2) and Sirius (2)

Italy
   Garibaldi (14)
Weight N/A
Elevation
(see Note 3)		 CPI
   Deck mountings:  -3 / +20 degrees
   Casemate mountings:  -3 / +15 degrees

PII
   Deck mountings:  -3 / +19 degrees
   Casemate mountings:  -3 / +15 degrees

HA mountings
   -3 / +53.5 degrees
Elevation Rate Manual operation, only
Train about +30 / +150 degrees in casemate mountings
about -150 / +150 degrees in open mountings
Train Rate Manual operation, only
Gun recoil N/A
Notes:

1) Mark I guns were used with CPI mountings while Mark II and III guns were used with PII mountings.

2) Many of the cruisers had a secondary battery of 4.7 (12 cm) guns that was later replaced with more 6" (15.2 cm) guns.  Powerful class was later given 12 guns.  Arrogant class later given 10 guns).  Eclipse class (except for Eclipse herself) were later given 11 guns.

3) A total of four CPI and twelve PII mountings were converted for AA use.  The Monitor Roberts was given a Mark I gun in one of these HA mountings in 1916.
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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
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 11" article in "Warship Volume VII" both by John Campbell
"British Battleships:  1860 - 1950" by Oscar Parkes
Page History

28 December 2008 - Benchmark
10 February 2009 - Added number of mountings information, added HA mounting note
31 December 2009 - Identified gunnery crew as being on HMS Ariadne
29 August 2011 - Added information on Trafalgar class and Superb