Mark IV tank

Mark IV
Mark IV male with unditching beam deployed
Type	Tank
Place of origin	United Kingdom
Service history
Used by	British Army  Imperial German Army Reichswehr  Imperial Japanese Army
Wars	First World War German Revolution of 1918–19
Production history
Designer	Major Walter Gordon Wilson
Manufacturer	see text
Unit cost	about £5,000
Produced	May 1917 – end 1918
Number built	1,220
Specifications
Weight	29 tons (28.4 tonnes) Female: 27 tons (27.4 tonnes)
Length	26 ft 5 in (8.05 m)
Width	Male: 13 ft 6 in (4.12 m)
Crew	8
Armour	0.25– 0.47 inches (6.1–12 mm)
Main armament	Male: Two 6-pounder (57-mm) 6 cwt QF guns with 332 rounds Female: five .303 Lewis guns
Secondary armament	Male: Three .303 in Lewis guns
Engine	Daimler-Foster, 6-cylinder in-line sleeve valve 16 litre petrol engine 105 bhp at 1,000 rpm
Transmission	Primary: 2 Forward, 1 Reverse Secondary – 2 speed
Fuel capacity	70 Imperial gallons
Operational range	35 mi (56 km)
Speed	4 mph (6.4 km/h)

The Mark IV (pronounced "Mark Four") was a British tank of World War I. Introduced in 1917, it benefited from significant developments on the first British tank (the intervening designs being small batches used for training). The major improvements were in armour, the re-siting of the fuel tank, and easier transportation. A total of 1,220 were built: 420 "Males", 595 "Females" and 205 Tank Tenders (unarmed vehicles used to carry supplies), which made it the most produced British tank of the War.

The Mark IV was first used in mid 1917 at the Battle of Messines Ridge. It remained in official British service until the end of the War, and a small number served briefly with other combatants afterwards.

The director of the Tank Supply Department, Albert Gerald Stern, first intended to fit the Mark IV with a new engine and transmission. Production of battle tanks was halted until the new design was ready, necessitating the use of the Mark II and III as interim training tanks. Failing to complete development soon enough to start production in time to have 200 tanks ready for the promised date of 1 April 1917, Stern was ultimately forced to take a Mark IV into production in May 1917 that was only slightly different from the Mark I tank.

The Mark IV Male carried three Lewis machine guns – one in the cab front and one in each sponson – and a QF 6 pdr 6 cwt gun in each sponson, with its barrel shortened as it had been found that the longer original was apt to strike obstacles or dig into the ground. The sponsons were not mirror images of each other, as their configuration differed to allow for the 6 pdr's gun-layer operating his gun from the left and the loader serving the gun from the right. The guns had a 100 degree arc of fire but only the starboard gun could fire straight ahead. The Female had five machine guns. Two of the machine guns were operated by the gun loaders.

The decision to standardise on the Lewis gun was due to the space available within the tanks. Despite its vulnerable barrel and a tendency to overheat or foul after prolonged firing, the Lewis used compact drum magazines which could hold up to 96 rounds. The Hotchkiss was fed from a rigid strip which was trimmed down to only 14 rounds for tank use; no sooner had the machine gunner guided the fall of shot onto the target then it was time to change the strip and the process repeated. It was not until a flexible 50 round strip was fully developed in May 1917 that the Hotchkiss would become the standard machine gun for tanks again. The changes caused delays, such as adapting the design for the bulky Lewis cooling barrel, and later, problems when the Hotchkiss strips had to be stored in positions designed for Lewis gun magazines.