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3.7 inch Mountain Howitzer

Gun

Mk 1
Mk 1/1 - Introduced 1944 with simplified breech mechanism
Mk 1/2 - Introduced 1945, new firing pin unit
Mk 1/3 - Obsolete 1960

Carriage

Mk 1 - Split trail, wooden wheels, pack carriage
Mk 2 - As Mk 1 with fittings for animal draught
Mk 3 - As Mk 2 but with fixed spades
Mk 4P - Pneumatic tyred
Mk 5 - Light version for airborne use

Data

Wt gun & breech mech - 451.5 lb
Wt breech section - 247 lb
Wt chase section - 204.5 lb
Wt in action - 1,856 lb
Total length - 46.8 inches
Length of bore - 43.5 inches
Rifling - 28 grooves uniform RH 1/25
Breech mech - Interrupted screw
Elevation - minus 5 to plus 40
Traverse - 20 L&R
Recoil system - Hydropneumatic variable
Recoil length - 17.5 to 35 inches

Introduced, officially, in February 1917 the gun broke down into several loads for either man or mule packing. The barrel was in two halves joined by a junction nut. Used during WW2 mainly in the Far East and Italy, it equipped the mountain batteries and was also used by the airborne artillery until replaced by the US 75 mm Howitzer. It was not declared obsolete until 1960.

Performance

With 20 lb Shrapnel shell:
Muzzle velocity - 973 ft/sec
Max range - 6,000 yds
With 20 lb HE shell (max Charge 4)
Muzzle velocity - 798 ft/sec
Max range - 4,500 yds

Ammunition

Shell HE Mk 3 - Amatol filled. Restricted to charge 4 or less
Shell Shrapnel Mk 6 - Nose ejecting filled with lead/antimony bullets
Shell Smoke Bursting Mk 3 - White phosphorus filled
Shell Smoke Base Ejection Mk 1 - Rarely seen
Shell Star Mk 3 - Star unit & parachute with Fuze Time & Percussion No 221T
Shell HEAT Mk 1 - Developed 1942

Propelling Charge
5 part in 3.6 inch long brass case