5"/42 (12.7 cm) BL Marks I, II, III, IV and V
Updated 07 December 2011

The different marks of these guns all had nearly the same ballistic performance, but they were of varying construction.  They were not considered very effective and were replaced by the much better 4.7" (12 cm) QF Mark I on newer ships.  A total of 112 guns were kept in storage for possible use on armed merchant cruisers until after World War I.

Some surplus naval guns were allocated as coast defense drill guns, but few were actually used in that role.

The Mark I had an A tube which included the breech block, 4 hoops and a trunnion hoop over the breech end.  This Mark was withdrawn from service after the similar 6" (15.2 cm) Mark II failed in the corvette HMS Cordelia in 1892.  The other marks had an A tube and jacket which included the breech block and included the trunnions.  They differed in the number and arrangement of hoops and tubes over the A tube between the jacket and muzzle.  Mark II and Mark III were later chase hooped to the muzzle while the Mark IV and V were constructed with these in place.  All were originally built with three-motion breech mechanisms.  Altogether, 77 Mark I, 150 Mark II, 225 Mark III, 100 Mark IV and 82 Mark V were manufactured.

Twelve guns were later converted to drill guns by replacing the breech mechanism with a single motion Welin breech block.  These were then redesignated as 5"/25 BLC Marks I/IV and Marks I/V.  A breech ring was added and the trunnions repositioned.  These changes also allowed an increase in muzzle velocity.  One of these guns still survives in the Ordnance Museum at Priddy's Hard, Portsmouth.

These guns should not be confused with the later 5" (12.7 cm) field pieces also known as 60 pdrs nor should they be confused with the Australian coast defense guns which included EOC Pattern D 5"/31 (12.7 cm) guns.

The data that follows is specifically for Marks IV and V, but the other marks were similar.


5"/25 (12.7 cm) Mark III gun on Vavasseur Mark I (VCPI) slide mounting
This gun was originally mounted on HMS Gannett and is now at the World Naval Base, formerly Chatham Naval Dockyard, Kent
Picture copyrighted by Bob Cordery of Colonial Wargamming

Gun Characteristics
Designation 5"/25 (12.7 cm) Marks I, II, III, IV and V
Ship Class Used On
(see Note)
Sloops and cruisers of the 1880s
Date Of Design About 1875
Date In Service About 1878
Gun Weight 2.005 tons (2.04 mt) including breech mechanism
Gun Length oa 139.15 in (3.534 m)
Bore Length 125 in (3.175 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume 504 in3 (8.256 dm3)
Rate Of Fire about 10 rounds per minute
Note:  It had been intended to arm the Nile, Trafalgar, Scout and Fearless with these guns, but they were completed with the much better 4.7" (12 cm) QF guns.
Type Bag
Projectile Types and Weights HE - 50 lbs. (22.7 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge
(see Note)
4.45 lbs. (2.02 kg) Cord 7.5
Muzzle Velocity
(see Note 1)
1,750 fps (533 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun 100 rounds
Note:  BLC Mark I/IV and I/V drill guns had their muzzle velocities increased to 1,905 fps (581 mps).
Elevation With 50 lbs. (22.7 kg) HE Shell
Range @ 19.7 degrees 8,700 yards (9,510 m)
Armor Penetration with 50 lbs. (22.7 kg) Projectile
Range Vertical Iron Plate
1,000 yards (9,140 m) 6.1 in (15.5 cm)
Note:  Data from "British Battleships:  1860 - 1950."
Mount / Turret Data
Designation Single Mountings
   Iris (13 - as rearmed), Caroline (?), Pylades (?) and Garnet (?):  VCPI, VBI and VBII
Weight  N/A
Elevation VCPI:  -5(?) / +20 degrees
VBI:  -5(?) / +15 degrees
VBII:  -5(?) / +22 degrees
Elevation Rate Manually operated, only
Train about -150 / +150 degrees
Train Rate Manually operated, only
Gun recoil N/A
Note:  These guns were used by many of the "masted cruisers" and RML armed ironclads of the late 1800s, but I lack details as to which ones and how many guns were carried.
Data from
"British Naval Guns 1880-1945 No 14" article in "Warship Volume VIII" by John Campbell
"Cruisers of the Royal and Commonwealth Navies" by Douglas Morris
"British Battleships:  1860 - 1950" by Oscar Parkes
Page History

22 July 2006 - Benchmark
30 January 2009 - Added links, added "not to be confused with" information, added Mount / Turret data
07 December 2011 - Corrected typographical errors