4"/40 (10.2 cm) BL Mark VIII and Mark XI
Updated 16 June 2012

The Mark VIII was introduced on the "Special Flotilla Leader Destroyer" Swift and subsequently used on many pre-World War I destroyers.  Some guns were modified for HA use during World War I.

Following the war, four guns were sent to the Caspian in 1919.  During World War II, many guns were used to arm DAMS merchantmen.

The Mark XI was the Mark VIII adapted for submarine use.

The Mark VIII was constructed of A tube, breech piece, B tube to the muzzle, wire over the breech piece, jacket, breech ring and bush screwed into the breech piece.  Used a Welin block with a "pure couple" breech mechanism.  Later guns and the Mark XI had a tapered inner A and A tube instead of the A tube, B tube and Breech piece.  Firing could be via either percussion or electrical means.  Actual bore length of all guns was 39.8 calibers.  When worn, the guns were repaired by boring out a part of the A tube and inserting a tapered liner.

A total of 246 of the Mark VIII guns were produced, of which 194 still remained in 1939.  Thirty Mark XI guns were manufactured, all of which were apparently scrapped by 1939.


HMS Swift
The paired 4" (10.2 cm) guns on the bow were later replaced with a single 6"/45 (15.2 cm) Mark VII gun


HMAS Warrego
Photograph from Allan C. Green collection of glass negatives
State Library of Victoria Image H91.250/1221

Gun Characteristics
Designation 4"/40 (10.2 cm) BL Mark VIII
4"/40 (10.2 cm) BL Mark XI
Ship Class Used On
(see Note 1)
   Destroyers:  Swift, later Tribals starting with Saracen, first 13 members of the K class, Acasta class members Acasta, Midge and Spitfire
   Submarines:  E2, E11, E12, E14, E21 and E25
   "Fly" class river gunboats
   Some P ships and Q ships
   Australian Swan class

Mark XI
   Submarines:  J1, K1-4, K6-16
   Some Q ships

Date Of Design About 1904
Date In Service 1908
Gun Weight 1.296 tons (1,317 kg)
Gun Length oa 166.4 in (4.227 m)
Bore Length 159.2 in (4.044 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist Uniform RH 1 in 30
Chamber Volume 298 in3 (4.88 dm3)
Rate Of Fire About 6 - 8 rounds per minute

1) The Japanese destroyer Sakaki carried one of these guns in 1918.  This was probably installed when she was rebuilt after being torpedoed by the Austrian submarine U.27 in 1917.

2) Modified HA guns were used on the K class destroyers, Acasta, Midge and Spitfire (one gun).

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:  5.38 lbs. (2.4 kg) MD16
World War II:  5.5 lbs. (2.5 kg) SC103
Muzzle Velocity 2,287 fps (697 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
Note:  Projectiles were 3crh.
Elevation With 31 lbs. (14.1 kg) HE Shell
Range @ 20 degrees 10,210 yards (9,340 m)
Mount / Turret Data
Designation Single Mounts
   Mark VIII (LA)
      Swift (4), Tribals (2) and K (3):  CPIII, CPIII*, CPV and CPVII
   Mark VIII (HA)
      K (3), Acasta (3), Midge (3) and Spitfire (1):  N/A

   Mark XI
      J 1 (1), K (2):  SI

Weight  N/A
Elevation All except HA conversions:  -10 / +20 degrees
HA conversions:  N/A, but probably about -10 / +70 degrees
Elevation Rate Manually operated, only
Train CP type:  360 degrees
SI:  About -120 / +120 degrees
Train Rate Manually operated, only
Gun recoil N/A
Note:  HA mountings had a "trap door" gun pit which allowed higher elevations by letting the breech go below the mounting deck level.  These guns were carried on a few K class destroyers and on the Acasta class destroyers Acasta, Midge and Spitfire (one gun).
Data from
"Warrior to Dreadnought:  Warship Development 1860-1905" and "The Grand Fleet:  Warship Design and Development 1906-1922" both by D.K. Brown
"Naval Weapons of World War Two" and "British Naval Guns 1880-1945 No 17" article in "Warship Volume X" both by John Campbell
The World War I Document Archive
Page History

16 October 2008 - Benchmark
30 January 2009 - Updated HMS Swift picture caption to include link, added information in the Mount / Turret "Designation" section
29 February 2012 - Added mounting information
16 June 2012 - Added picture of HMAS Warrego