4"/40 (10.2 cm) QF Marks I, II and III
Updated 03 February 2014

The 3"/50 (7.62 cm) secondary weapons of HMS Dreadnought were felt to be too small a caliber to be effective as an anti-torpedo boat gun.  For that reason, these 4"/40 (10.2 cm) guns were used on the Invincible class battlecruisers.  However, these guns were found to be too weak and they were in turn replaced with the more powerful 4"/50 (10.2 cm) Mark VII during World War I.

During World War II, many of these guns were used on minor warships and some of the older destroyers.  Some were also employed in coastal batteries.

The Mark I and Mark III had similar ballistic performance, but differed in construction.  The Mark I had an A tube with short chamber liner, half length wire, full length jacket and a screw breech ring connected the jacket to the breech bush over the A tube.  Mark IA differed in that the A tube was thicker over the front of the chamber.  The Mark III had an A tube, wire of reduced length, B tube and jacket with a screwed C hoop connecting them.  Ten Mark I, eight Mark IA and 261 Mark III guns were manufactured.  There were also seven Mark I/III built like the Mark III but with the breech ring and bush as the Mark I.  Five of these were later converted entirely to the Mark III design and then designated as the Mark III*.

The Mark II was a trunnioned gun of the same performance as the Mark I.  Eight guns were made to rearm the old battleship Temeraire and the paddle steamer Sphinx.


HMS Inflexible
4"/40 (10.2 cm) guns can be seen on top of "A" and "X" turrets
IWM photograph Q 39267

Gun Characteristics
Designation 4"/40 (10.2 cm) QF Marks I, II and III
Ship Class Used On Invincible class, Amethyst and Pelorus light cruiser classes, various sloops and gunboats
Date Of Design About 1904
Date In Service 1908
Gun Weight 2,952 lbs. (1,339 kg)
Gun Length oa 165.3 in (4.199 m)
Bore Length 160 in (4.064 m)
Rifling Length 143.5 in (3.645 m)
Grooves 24
Lands N/A
Twist N/A
Chamber Volume 213 in3 (3.49 dm3)
Rate Of Fire about 8 - 10 rounds per minute
Type Separate
Projectile Types and Weights HE - 25 lbs. (11.3 kg)
HE - 31 lbs. (14.1 kg)
Bursting Charge N/A
Projectile Length N/A
Propellant Charge
(see Note 1)
3.56 lbs. (1.6 kg) Cord 15
5.11 lbs. (2.3 kg) MD16
Muzzle Velocity Small HE - 2,370 fps (722 mps)
Large HE - 2,300 fps (701 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun
(see Note 2)
Invincible:  100 rounds
Others:  N/A

1)This may have been the only gun for which Cordite MD was made in a tubular form as well as in cords.

2) Original outfit for Inflexible was 50 CP and 50 HE, later changed to 30 CP and 70 HE.

Elevation With 25 lbs. (11.3 kg) or 31 lbs. (14.1 kg) HE Shell
WWI Range @ 20 degrees 9,600 yards (8,780 m)
Mount / Turret Data
Designation Single Mountings:
   Amethyst (12) and Pelorus (8):  PI
   Invincible (16):  PI*
Weight  N/A
Elevation PI:  -10 / +20 degrees
Elevation Rate Manually operated, only
Train 360 degrees
Train Rate Manually operated, only
Gun recoil N/A
Note:  Invincible was sunk with these guns but Indomitable was rearmed with the 4"/45 (10.2 cm) Mark VII in April 1917and Inflexible was rearmed with the 4"/45 (10.2 cm) Mark IX in July 1917.
Data from
"British Battleships of World War One" by R.A. Burt
"Warship Special #1:  Battlecruisers," "Technical Topics No 5:  Cordite" article in "Warship Volume II"  and "British Naval Guns 1880-1945 No 18" article in "Warship Volume X" all by John Campbell
"Battlecruisers" by John Roberts

Page History

25 February 2007 - Benchmark
10 January 2009 - Added remark concerning tubular cordite
12 February 2012 - Updated to latest template and added mounting information
03 February 2014 - Added ammunition stowage information, photograph of Inflexible and note about rearming of Indomitable and Inflexible