BL 8-inch howitzer Mk VI – VIII

BL 8-inch howitzer Mk VI, VII, VIII
US-built version of Vickers BL 8-inch howitzer Mk 6 outside the War Museum in Helsinki, Finland
Type	Heavy howitzer
Place of origin	United Kingdom
Service history
In service	1916–1943
Used by	United Kingdom Australia Canada Russian Empire Finland United States
Wars	World War I, World War II
Production history
Designer	Vickers
Designed	1915
Manufacturer	Vickers Armstrong Beardmore Woolwich Midvale Steel, major assemblies by Hadfield and Beyer Peacock.
No. built	711 equivalent complete equipments(UK contracts).
Specifications
Weight	8.74 tonnes
Barrel length	Mk VI: 9 feet 9 inches (2.972 m) Mk VII & VIII: 11 feet 6 inches (3.505 m)
Shell	HE 200 lb (91 kg)
Calibre	8-inch (203.2 mm)
Breech	Welin interrupted screw with Asbury mechanism
Recoil	Hydro-pneumatic recuperator, hydraulic buffer
Carriage	Wheeled, box trail
Elevation	Mk VI: −4° to 50° Mk VII & VIII: 0° to 45°
Traverse	4° L & R
Muzzle velocity	Mk VI: 1,300 ft/s (400 m/s) Mk VII & VIII: 1,500 ft/s (460 m/s)
Effective firing range	Mk VI: 10,745 yd (9,825 m) Mk VII & VIII: 12,300 yd (11,200 m)

The BL 8-inch howitzer Marks VI, VII and VIII (6, 7 and 8) were a series of British artillery siege howitzers on mobile carriages of a new design introduced in World War I. They were designed by Vickers in Britain and produced by all four British artillery manufacturers, but mainly by Armstrong, and one American company. They were the equivalents of the German 21 cm Morser 16 and in British service were used similarly to the BL 9.2-inch howitzer, but were quicker to manufacture, and more mobile. They delivered a 200 lb shell to 12,300 yards. They had limited service in the British Army in World War II before being converted to the new 7.2-inch calibre. They also equipped a small number of Australian and Canadian batteries in World War I and by the US Army in that war. They were used in small numbers by other European armies.

8 inch was a calibre adopted in the First World War by the British Army. The Marks VI, VII and VIII (6, 7 and 8) were a new design and not related to the stopgap early Marks 1–5 of 8-inch howitzer, which used shortened and bored-out naval 6-inch gun barrels.

The Vickers design, very similar to their 6-inch howitzer, was approved in August 1915 and first substantial order placed in March 1916 for 50 howitzers, with 30 more in the autumn. It was 4–5 tonnes lighter than the improvised 8-inch "howitzers" Mks I – V. The Mk VI barrel was of built-up construction and was 14.7 calibres (117.7 inches) long, with a range of 10,745 yards (9,825 m).

Introduced July 1916. Mk VII had a longer barrel (17.3 calibres, or 138.4 inches) of wire-wound construction and increased the range to 12,300 yards (11,250 m). The new barrels turned out to have short lives and suffered from cracked A tubes (the inner rifled layer of the built-up barrel).

Mk VIII incorporated various small improvements and a thicker and stronger barrel.

Early problems of stability on very hard or soft ground became apparent with the Mk VI, leading to the recoil system not functioning correctly. A Commission went to France to investigate, and a special level "Vickers platform" was adopted, to which the wheels and trail were secured for accurate shooting. A major change in the line of shooting required the platform to be relaid. Setting up and adjusting the platform was labour-intensive. The US manual describes it: