Flying Elephant The Flying Elephant was a proposed super - heavy tank , planned but never built by the British during World War I . Development . After the last order for an additional fifty Mark I vehicles in April 1916 , it was not certain that any more tanks were to be produced . Everything would depend on the success of the new weapon . William Tritton , co - designer and co - producer of the Mark I , thought he already understood what would prove to be its main weakness . A direct hit by a shell would destroy the vehicle , a major drawback on a battlefield saturated with artillery fire . Tritton decided to design a tank that would be immune to medium artillery fire in April 1916 . Tritton was unsure what this would entail . He did not know how thick the armour should be to ensure complete protection . The same month Lieutenant Kenneth Symes began to test two - inch ( 51 mm ) armour plate by firing at it with various captured German guns . In June , this programme was expanded by testing several types of plate at Shoeburyness , delivered by armour producer William Beardmore and Company . The Tank Supply Committee approved the production of a prototype on 19 June 1916 , but the design was not to be finalised until late August 1916 . Description . Partial drawings have survived and show a vehicle long and about tall and three metres wide , not that much larger than the Mark I . However , the weight was estimated at roughly a hundred tons , much heavier than the 28 tons of the Mark I . The huge increase in weight came from the enormously thick armour for the time ( three inches at the front , two inches on the sides ) . The hull roof consisted of a horizontal half - cylinder , apparently also with a uniform armour two inches thick . The front was a vertical half - cylinder , the transition between the two being a half - dome . Many sources claim that the main armament , a nose - mounted cannon , was a standard 57 - millimetre 6 - pounder gun . However , John Glanfield , in his history " The Devil ' s Chariots " , states that it was a 75 - millimetre , or 13 - pounder gun . A 6 - pounder main gun for such a heavy machine would have meant half the main armament of contemporary vehicles . The preliminary design , for which partial blueprints are in the Albert Stern archive at King ' s College London , featured two six - pounders in sponsons either side of a bulbous nose equipped with no fewer than five machine guns . Each side had two machine - gun positions on the flanks , with two more at the rear ( the original Foster drawings make this quite clear ; the reproduction of the drawings in David Fletcher ' s book " British Tanks 1915 – 19 " is cropped and makes the rear guns ambiguous in nature ) . Originally , the shell - proof tank was referred to simply as the Heavy Tank , then Foster ' s Battle Tank . Where the nickname ' Flying Elephant ' came from no one knows for sure , though it was probably the result of the trunk - like nose gun , domed front , and enormous bulk combined with a traditional British lightheartedness . The tank was fitted with two pairs of caterpillar track s . The outer tracks resembled those of the Mark I , but were flatter and 61 centimetres wide , while a pair of additional , narrower tracks were fitted to the underside approximately 6 inches higher than the main tracks . They were not intended to be used for normal driving but were to be engaged to give extra traction over rough ground and would have helped to prevent " bellying " , i . e . the tank becoming stuck on higher ground between the two outer tracks . All four tracks could be simultaneously driven by two Daimler 105 horsepower ( 78 kilowatt ) engines , positioned on the centre - line , with the inner tracks connected to the main units via dog clutch es . Each engine had its own primary gearbox , both of which drove into one single differential . This differential powered two secondary gearboxes , one for each main track . This differs from the solution chosen for the later Whippet in which each engine drove its own track . Results . It is certain that construction was started at some point , but did not result in a completed prototype . Albert Gerald Stern , the head of the Tank Supply Department , wrote that the War Office ordered the end of the project late in 1916 , because it deemed mobility more important than protection . Historian David Fletcher speculated that the project ran into trouble because the vehicle was grossly underpowered ; top speed was estimated at two miles per hour , and it seems unlikely that it could have worked itself free when stuck in mud . The fact that the Mark I series turned out to be a success removed one of Tritton ' s main motives for building the heavier tank . However , John Glanfield writes that Tritton , in an effort to lighten the machine and make it more practicable , halved the thickness of the armour , reducing the overall weight to a still hefty 50 – 60 tons . Its appearance would have remained unchanged . Furthermore , the role of the Flying Elephant was changed from a vague ' attack ' role to that of a ' tank - buster ' when it was feared that the Germans were developing their own armoured fighting vehicle s . Apparently , Stern planned to build twenty of the machines , before the project was cancelled .