BL 9.2-inch howitzer

BL 9.2-inch howitzer
Australian Battery of 9.2 inch Mark I howitzers in action at Fricourt during the Battle of the Somme, August 1916.
Type	Heavy siege howitzer
Place of origin	United Kingdom of Great Britain and Ireland
Service history
In service	1914–1945
Used by	United Kingdom Australia Canada United States Belgium Russian Empire
Wars	World War I, World War II
Production history
Designer	Mk I : Coventry Ordnance Works Mk II : Vickers
Designed	1913
Manufacturer	Vickers, Bethlehem Steel
Produced	1914–1918
No. built	All Mks equivalent to 632 complete equipments plus 43 ordnances (UK contracts)
Variants	Mk I, Mk II
Specifications
Weight	Mk II Body, cradle & ordnance only 5 tons 17 cwt
Barrel length	10 ft 1 in (3 m) (Mk I) 13 ft 3 in (4 m) (Mk II)
Shell	HE 290 lb (130 kg)
Caliber	9.2-inch (233.7 mm)
Breech	Welin breech block with Smith-Asbury mechanism
Recoil	Variable Hydro-pneumatic 23-40 inches (MK I) 20-44 inches (MK II)
Carriage	Siege carriage
Elevation	15°–55° (Mk I) 15°–50° (Mk II)
Traverse	30° L & R
Muzzle velocity	1,187 ft/s (362 m/s) (Mk I) 1,600 ft/s (490 m/s) (Mk II)
Maximum firing range	10,060 yd (9,200 m) (Mk. I) 13,935 yd (12,742 m) (Mk. II)

The Ordnance BL 9.2-inch howitzer was a heavy siege howitzer that formed the principal counter-battery equipment of British forces in France in World War I. It equipped a substantial number of siege batteries of the Royal Garrison Artillery. It remained in service until about the middle of World War II.

The origins of a British heavy "siege" howitzer lie in advances in technology and the 21 cm howitzers used by the German field army. UK had purchased Skoda 9.45-inch howitzer from Austria in 1900 for service in South Africa. A practice camp in the 1900s showed this howitzer's high minimum elevation was a major problem. In due course Britain decided to develop its own heavy weapon, but retained the Skoda transport technique of moving it in three loads on wheeled trailers (either horse- or tractor-towed). A trial gun was received in 1913 and fired at Woolwich and Shoeburyness during the winter. In July 1914 it was sent to the tactical firing range at Rhyader with a siege company. The assessment was "This equipment is a vast improvement on any other in use in the siege artillery, and is worth taking with an army." Major General von Donop, Master-General of the Ordance, immediately ordered 16 guns and a further 16 were ordered in October 1914. The prototype gun, "Mother", was in action in France on October 31, 1914 and production guns entered service in 1915.

The gun was transported in three loads - body and cradle, bed, barrel - towed by either heavy horses or a Holt tractor. The equipment comprised a segment shaped ground platform assembled from steel section and bolted to a holdfast sunk flush with the ground. An earth box fitted above ground to the front of the holdfast, with 9 long tons (9,100 kg) (Mk 1) or 11 long tons (11,200 kg) (Mk 2) of earth prevented it "bucking". On soft ground, extra beams were used under the holdfast. The carriage was mounted on the platform, it was pivoted at the front and traversed up to 30 degrees left and right by a spur gear engaging a curved toothed rack at the breech end of the platform, with the weight of the carriage on rollers.

The tubular cradle pivoted by the trunnions supported the barrel – a wire bound A tube – and connected it to the hydro-pneumatic recoil system with a floating piston (the first British use of this) and hydraulic buffer. However, the initial design suffered from excessive recoil and was modified in 1916. In 1917 the recoil was further improved by addition of a recoil indicator and cut-off gear. Full recoil (40-inch Mk I, 44-inch Mk II) was allowed at lower elevation, hence absorbing most of the horizontal (i.e. backward) force. A shorter recoil (23-inch Mk I, 20-inch Mk II) was allowed at high elevation where the ground itself could absorb much of the vertical (i.e. downward) recoil force. This prevented the breech from hitting the platform. The barrel had to be depressed 3° for loading, as can be seen in the photograph, shown below, of a howitzer of the Australian 55th Siege Battery.