Mark IV Tank - Development

Development

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.

The Mark IV Male carried three Lewis machine guns - one in the hull front and two in the sponsons - as well as the two sponson guns (now shorter barrelled QF 6 pdr 6 cwt guns). The Female had five machine guns. Two of the machine guns were operated by the gun loaders.

The decision to standardize 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.

This tank introduced the use of the fascine, a bundle of brushwood, bound with chains, about 10 ft (3.0 m) long and 4.5 ft (1.4 m) in diameter carried on the front. It was dropped into trenches to allow the tank to more easily cross over.

A large number of these tanks were also used for development work. In an attempt to improve trench-crossing capability, the tadpole tail was introduced, an extension to the rear track horns. However, it proved insufficiently rigid and does not appear to have been used in combat. Other experimental versions tested radios, mortars placed between the rear horns, and recovery cranes. Some of these devices were later used on operational tanks. Mark IVs were also the first tanks fitted with unditching beams by field workshops. A large wooden beam, reinforced with sheet metal, was stored across the top of the tank on a set of parallel rails. If the tank became stuck, the beam was attached to the tracks (often under fire) and then dragged beneath the vehicle, providing grip.

• Crew
  • 8
• Combat Weight
  • Male: 28 tons (28.4 tonnes) - Female: 27 tons (27.4 tonnes)
• Armour
  • 0.25–0.47 in (6.1–12 mm)
• Armament
  • Three MG and two 6-pdrs (Male), Five .303 Lewis MG (Female)
• Ammunition storage
  • 6 pounder: 180 HE rounds and remainder Case