These were coast defense guns developed by the Army for use against German Schnellboots ("E-boats") and other small craft. The first prototypes were under test by 1928 and series production began in 1934. Twenty-two of them were transferred to the Navy and used on old destroyers detailed for coastal escort duties.
Constructed of A tube, part length jacket and breech ring. Used a semi-automatic sliding breech block. Guns were unusual in that the gun layers did not fire the weapons. Instead, the loader for each gun actuated a firing lever after the round was loaded.
"As a measure of the firepower of the Twin 6-pounder, a battery of them at the mouth of Valetta harbour sank five Italian torpedo boats and human torpedo attack vessels in less than two minutes on the night of 25/26th July 1941." - Terry Gander.
Constructed of A tube, part length jacket and breech ring. Used a semi-automatic sliding breech block.
| Designation | 6-pdr / 10cwt QF Mark I |
|---|---|
| Ship Class Used On | Destroyers Campbell, Mackay, Montrose, Whitshed, Wivern, Worcester, Walpole and Windsor |
| Date Of Design | N/A |
| Date In Service | 1941 in naval service |
| Gun Weight | 1,060 lbs. (481 kg) |
| Gun Length oa | 109.72 in (2.787 m) |
| Bore Length | 105.47 in (2.679 m) |
| Rifling Length | 86.55 in (2.198 m) |
| Grooves | (24) 0.012 in deep x 0.220 in (0.30 mm x 5.59 mm) |
| Lands | 0.074 in (1.9 mm) |
| Twist | Polygroove, plain section
Uniform RH 1 in 30 |
| Chamber Volume | 73.5 in3 (1.2 dm3) |
| Rate Of Fire | 18 rounds per minute 1 |
- ^Well-trained crews could achieve a ROF as high as 40 RPM from each barrel.
| Type | Fixed |
|---|---|
| Weight of Complete Round | N/A |
| Projectile Types and Weights | HE: 6.28 lbs. (2.85 kg)
HE-T: 6.54 lbs. (2.97 kg) |
| Bursting Charge | N/A |
| Projectile Length | N/A |
| Propellant Charge | 1.27 lbs. (0.576 kg) N 045 |
| Muzzle Velocity | HE: 2,386 fps (727 mps)
HE-T: 2,356 fps (718 mps) |
| Working Pressure | N/A |
| Approximate Barrel Life | N/A |
| Ammunition stowage per gun 1a | N/A 2a |
| Elevation | Distance |
|---|---|
| 45 degrees | 11,300 yards (10,330 m) |
| Designation | Twin Mounts
Coastal Defense: Mark I Destroyers (1): Mark I* 1b |
|---|---|
| Weight | N/A |
| Elevation | -10 / +80 degrees |
| Elevation Rate | Manually operated, only |
| Train | 360 degrees |
| Train Rate | Manually operated, only |
| Gun recoil | 12 in (30.5 cm) |
- ^The naval mounting had a more extensive shield than did the coast defense mounting.
"Naval Weapons of World War Two" by John Campbell
"Warships of World War II" by H.T. Lenton and J.J. Colledge
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"Twentieth Century British Coast Defence Guns" by Terry Gander
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Special help from Dave Alton and Richard Worth
16 October 2005 - Benchmark
12 February 2012 - Updated to latest template
15 December 2013 - Added photographs of HMS Mackay
03 May 2019 - Converted to HTML 5 format, reorganized notes and added to description and gun data and added Front View photograph
22 September 2025 - Redid photographs