Why Tanks Are Giant Caterpillars 



Armor? The Caterpillar has it. Traveling treads? The Cater- 

 pillc^r has them tcx). Machine guns? It has a poison squirt-gun 



By John Walker Harrington 



THE motion of the most formidable 

 and terrifying of modern war ma- 

 chines has often been compared with 

 that of the lowly larva from which comes 

 the radiant butterfly. This famed cruiser 

 of the battlefields might never have been, 

 but for the invention of the farm trac- 

 tor of Benjamin Holt with its caterpillar 

 tread. Through the courtesy of Captain 

 Haig, of the British Army, who is here 

 dem.onstrating the pride of the English 

 arms, the writer was permitted to spend 

 nearly an hour within the Britannia, and 

 at every point he was more and more im- 

 pressed with the idea that not only does 

 the tank resemble the caterpillar in 

 movement, but that there are strange 

 likenesses in structure, in armor, and 

 even in control between the two objects. 

 The tank is a high-powered, armored 

 automobile differing from the war motor- 

 car in that it moves not on wheels but on 

 two steel belts traveling on the heavy 

 metal frames on either side of its diamond- 

 shaped body. The belts consist of shoes 

 ingeniously linked together in endless 

 chains. Each shoe has a flange, with 

 which the tank can lay a firm hold on the 

 ground. The belts are fitted to heavy 

 sprockets. The rear sprockets are con- 

 nected by gearing with the powerful 

 engine in the back of the tank. The front 

 sprockets are idlers over which the belts 

 glide. There are also wheels which rest 

 on the upper surfaces of the belts. At 

 the top of the frames are rollers over 

 which the belts pass. The tank is really 

 laying down twin tracks or a railroad 

 of its own. 



The body of the average caterpillar 

 consists of thirteen segments, four of 

 which belong to his thorax or, dropping 

 into mechanical terms, his fore compart- 

 ment, while nine are assigned to the 

 abdominal section. The number of 

 segments varies with the species. The 

 chest portion has three pairs of true 

 legs, so culled because they are well 

 jointed, easily controlled and muscular. 



They are protected with horny sheaths 

 and are in effect armored. With these 

 true legs the caterpillar can steer him- 

 self, help himself along a twig, or seize 

 leaves. 



The pro-legs, or false legs, appear on 

 at least five of the segments, duly paired. 

 In their structure they resemble the shoes 

 of the tank belts to some extent and they 

 perform the same functions. They are 

 fleshy un jointed protuberances rather 

 than limbs. At the bottom of each one 

 are minute hooks which are used auto- 

 matically in giving the animal a hold on 

 the surface he is traversing. They are 

 for clasping, and in fact the rear pair are 

 so modified as to be called claspers. 

 Now, if a caterpillar could keep his pro- 

 legs or shoes moving over his head and 

 over his tail in an endless chain arrange- 

 ment, his resemblance to the tank as far 

 as the locomotion details are concerned 

 would be perfect. 



Some of the caterpillars have such a 

 rapid, undulating movement, that it is 

 hard at first to analyze its elements. The 

 caterpillar actually walks by extending 

 and contracting the fleshy segments of 

 his body, the power being transmitted 

 mostly to his pro-legs. 



Any one who has seen the fuzzy larvae 

 of the tussock moth going up a tree trunk 

 will reahze that the caterpillar is happy at 

 any angle. The same principle of construc- 

 tion illustrated in that insect permits the 

 tank almost to stand on end without los- 

 ing balance. 



For the sake of simplicity, the wheels 

 at the rear of the tank by which it was 

 once steered have been discarded and 

 the direction is given by running the two 

 belts at different speeds. The landship 

 is rudderless. The caterpillar can twist 

 his segments at the jointures. 



The observation facilities and guide 

 centres of both are in their forward com- 

 partments. The commander of a tank 

 and the driver sit well forward in the 

 Juggernaut, looking out of very narrow 



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