The British Mark IV "Male" heavy tank was an up-armored version of the Mark I, with all of its 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 and rails could be carried on the roof to act as an unditching beam.
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 April 1st, 1917. Ultimately he was forced to keep the Mark IV in production until May 1917, which was only slightly different from the Mark I.
The Mark IV "Male" carried 4 Lewis machine guns as well as the two sponson guns (now with shorter barrels). The "Female" version had six machine guns, with two of the machine guns were operated by the gun loaders. All told, some 1220 vehicles were built: 420 Males, 595 Females and 205 Tank Tenders which were supply tanks. Sold Out!