4"/50 (10.2 cm) BL Mark VII
Updated 03 February 2014

This weapon entered service on the dreadnought HMS Bellerophon and later replaced some of the 4"(10.2 cm) Mark I and Mark III guns used on older ships.

These weapons were installed in both casemates and in single open mounts on British dreadnoughts.  The open mounts were installed without shields but some ships had these added after 1917.  In 1918 a HA mounting using a reduced charge was introduced and most capital ships had one or two of these installed on a main caliber turret for anti-aircraft purposes.

During World War II these weapons were used on many minor warships and a considerable number were used as coastal artillery.

Mark VII was constructed of inner A and A tubes, wire wound, B tube to the muzzle with jacket, breech ring and breech bush screwed into the A tube.  Used a Welin breech block with "pure couple" breech mechanism.  Cannelured rings for reducing "steel choke" were placed between the shoulders of the A and inner A tubes.  Mark VII* was a single gun made by Beardmore with a different construction.  Mark VII** were fifteen guns with no inner A tube and with the B tube and jacket being combined.

Firing could be either percussion or electrical.  A total of 600 of these weapons were produced, of which 482 still remained in 1939.


4"/50 (10.2 cm) BL Mark VII on unidentified DEMS circa 1943
Canada Department of National Defence / Library and Archives Canada Photograph PA-116103


HMS Vanguard
4"/50 (10.2 cm) guns in superstructure and on "X" turret, the latter were not HA mountings


HMS Thunderer showing superstructure 4"/50 (10.2 cm) guns
Photograph copyrighted by D.K. Brown


HMS Temeraire showing 4"/50 (10.2 cm) Mark VII guns in the superstructure
IWM photograph SP 1771

Image at Australian War Memorial

Picture of 4"/50 (10.2 cm) Mark VII gun on HMAS Australia

Gun Characteristics
Designation 4"/50 (10.2 cm) BL Mark VII, VII** and VIII***
Ship Class Used On Bellerophon, St. Vincent, Neptune, Indefatigable, Colossus, Orion, Lion and King George V (1910) classes

Boadicea, Active and Bristol light cruiser classes plus smaller warships

Indomitable as rearmed

During World War II this weapon was used mostly on DEMS

Date Of Design About 1904
Date In Service 1908
Gun Weight 4,687 lbs. (2,126 kg)
Gun Length oa 208.5 in (5.295 m)
Bore Length 201.3 in (5.112 m)
Rifling Length 171.6 in  (4.359 m)
Grooves 32
Lands N/A
Twist Uniform RH 1 in 30
Chamber Volume 600 in3 (9.83 dm3)
Rate Of Fire about 6 - 8 rounds per minute
Type Bag
Projectile Types and Weights HE - 31 lbs. (14.06 kg)
CPC - 31 lbs. (14.06 kg)
Shrapnel - 31 lbs. (14.06 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge World War I:  9.37 lbs. (4.3 kg) MD16
World War I HA:  6.0 lbs. (2.7 kg) MD8
World War II:  9.7 lbs. (4.4 kg) SC103
Muzzle Velocity 2,864 fps (873 mps)
With HA charge:  about 2,400 fps (732 mps)
Working Pressure N/A
Approximate Barrel Life 1,200 rounds
Ammunition stowage per gun
(see Note 2)
Indomitable (as rearmed) and Indefatigable:  100 rounds
Bellerophon:  200 rounds
St. Vincent:  150 rounds (peace), 200 rounds (war)
Colossus, Neptune, Orion, Queen Mary, Lion and King George V:  150 rounds
Others:  N/A

1) Projectiles were 3crh.

2) Outfit for the Indefatigable class as commissioned and Indomitable as rearmed was 50 CPC and 50 HE, later 30 CPC and 70 HE, still later 25 CPC, 60 HE and 15 HE with night tracer.  Outfit for the Lion class as commissioned was 75 CPC and 75 shrapnel.  Later, she carried 160 HE and 40 Incendiary.

Elevation With 31 lbs. (14.1 kg) HE Shell
Range @ 15 degrees 11,600 yards (10,610 m)
Mount / Turret Data
Designation Single Mounts
   PII, PII*, PIV*, PIV**, PVI and PVIII
   HA Mark II

Bellerophon (16), St. Vincent (20), Neptune (16), Indefatigable (16), Orion (16), Lion (16) and King George V (16)

Indomitable as rearmed (12):  PVI

Weight  N/A
Elevation PII, PII* and PVI:  -7 / +15 degrees
PIV*, PIV** and PVIII:   -10 / +15 degrees
HA Mark II:  -10 (?) / +60 degrees
Elevation Rate Manually operated, only
Train Open mounts:  360 degrees
Casemate mounts:  About +30 to +150 degrees
Train Rate Manually operated, only
Gun recoil N/A
Data from
"The Grand Fleet:  Warship Design and Development 1906-1922" by D.K. Brown
"British Battleships of World War One" by R.A. Burt
"Warship Special No. 1:  Battlecruisers," "Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 17" article in "Warship Volume X" all by John Campbell
"Naval Weapons of World War One" By Norman Friedman
"British Battleships 1860 - 1950" by Oscar Parkes
"Battlecruisers" by John Roberts
The World War I Document Archive Handbook
Special Help from Rod Butcher

Page History

14 October 2008 - Benchmark
28 January 2010 - Added photograph of gun on DEMS
12 February 2012 - Updated to latest template
04 November 2012 - Added ammunition outfits for battlecruisers
03 February 2014 - Added ammunition outfits for battleships and photograph of Temeraire