5.5 inch Medium Gun

5.5 inch Medium Gun

In the early 1930’s discussions began on replacing the old 6 inch gun & 6 inch 26 cwt howitzer. An Operational Requirement was issued in January 1939 & it was discovered that the best calibre to meet the requirements was 5.5 inch.

There were many problems during the development and parts had to be re-designed & replaced. Because of this and problems organising production, the first 5.5 inch Medium Gun didn’t go into action in the Western Desert until May 1942. There were some objections to its lack of range but this was solved in 1943 when the standard HE shell was changed from 100 lbs to 80 lbs.

The service weapon was the Mark 3 gun. Marks 1 & 2 had been WW1 Navy weapons which bore no relationship to the army gun. Post war the Mark 4 was introduced with just a change to the taper in the chamber. The 5.5 inch Medium Gun remained in British service until 1980 although it continued in service with other nations for much longer.


Mk 3Auto-frettaged loose barrel in a short jacket. Asbury interrupted Welin screw
breech, percussion fired.
Mk 4Alteration to the angle of shot seating in the chamber. Introduced in 1948.


Marks 1 & 2
(only differences
are a change from
rivetted to welded
Split trail with hydropneumatic recoil system. Hydropneumatic
balancing cylinders in 2 vertical mounts to balance the barrel mass.
Because of leakage problems these were changed to springs.
Trough cradle with trunnions towards the rear to allow recoil at full
elevation. Quick loading gear.


No.1Detachment Commander
No.2Breech Operator – fires gun
No.4Load & Ram
No.5Load & Ram
No.6Prepare cartridges
No.7Prepare shells
No.8Prepare shells
No.9Prepare shells
No.10Coverer, supervise ammunition


Weight of gun & breech mechanism4,120 lbs
Total length171.6 inches
Length of bore164 inches (30 calibres)
Rifling36 grooves, uniform right hand 1/25
Breech mechanismAsbury interrupted screw, percussion fired
Elevation– 5° to +45°
Traverse30° left & right
Recoil systemHydropneumatic, variable, 30 inches to 54 inches
Weight in action13,646 lbs


Firing 100 lb HE shell
Muzzle Velocity1,675 feet/second
Maximum Range16,200 yards
Firing 80lb HE shell
Muzzle Velocity1,950 feet/second
Maximum Range18,100 yards


Separate loading, bag charge

Shell, HE, S/L, 100lb Mk 1DStreamlined shell with single, wide, driving band. Could be
fitted with Fuze, Precussion, 119 or 231
Shell, HE, S/L, 100lb Mk 2DSame as Mk 1D except had double driving bands for better
sealing in the bore.
Shell, HE, S/L, 80lb Mk 1DAlmost the same size as the 100lb shell. Double driving
bands & painted black from the bands to the rear. This
indicated it was an 80lb shell.
Shell, Smoke, BE, Mk 1DRarely issued, it used a Time & Percussion Fuze No. 221
Shell, Coloured Smoke,
BE, Mk 1D
Not produced until September 1945. Unlikely to ever had
been issued to service regiments.
Propelling ChargeOriginally a four charge system. Charge 1 for short range with Charge 2 as an increment. Charge 3 for long range with Charge 4 as an increment.
A Super Charge was introduced with the 80lb shell. It was never fired with the other charges.
The Royal Artillery 1939-45