| An up-armoured version of the Mark I with all fuel stored in a single external tank (located between the rear track horns) in an attempt to improve crew safety. The sponsons could be pushed in to reduce the width of the tank for rail transportation. Rails on the roof carried an unditching beam. One-thousand two-hundred twenty were built: 420 Males, 595 Females and 205 Tank Tenders, which were supply tanks. 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 Mark II and III as interim training tanks. He failed however to complete development soon enough to start production in time to have 200 tanks ready for the promised date of 1 April 1917. He was ultimately forced to take a Mark IV in production in May 1917 that was only slightly different from the Mark I. The Mark IV Male carried four Lewis machine guns as well as the two sponson guns (now QF 6 pdr 6 cwt with shorter barrels). The Female had six machine guns. Two of the machine guns were operated by the gun loaders | 
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