714 



Popular Science Monthly 



surmount seemingly impassable obstruc- 

 tions, such as trees, boulders, ditches, shell 

 craters, wire entanglements or trenches. 

 Harveyized steel, so named after its in- 

 ventor, made the tanks impervious to 

 machine gun and rifle fire, shrapnel and 

 everything except a direct shell hit. 



How a Tank Is Built 



The principal \ 

 feature of the 

 tank's construe- \ 

 tion is the cater- 

 pillar or track-lay- 

 ing device. This 

 consists of an end- 

 less steel belt made 

 up of short sec- 

 tions like shoes, 

 which lie flat on 

 the ground. These 

 support the vehi- 

 cle wheels which 

 mounted 



are mountea on 

 trucks somewhat similar to those on rail- 

 way cars. The insides of the shoes have 

 double rails over which the truck wheels 

 run as shown in the illustration at the top 

 of page 712. 



The endless chain made up of the shoes 

 acts as a track, being laid flat under the 



The caterpillar tread is curved up in the arc of a 

 huge circle at the front which gives the vehicle its 

 wonderful tractive p>owers. This large curvature 

 acts as a huge wheel with a tremendously long 

 leverage equal to the radius of the circle or the 

 six)kes of the imaginary wheel of the same di- 

 ameter^ Only that portion of the assumed wheel 

 which would come in contact with the ground acts 

 as the lever, and it is just this portion that is 

 reproduced in the front end of a caterpillar belt 



wheels and picked up again after the wheels 

 have passed over it. The endless chains 

 are driven by means of sprockets on the 

 rear axle of the tank. 



The real unusual adaptation of the cater- 

 pillar device for which the British designer 

 of the tanks must be given credit is the 

 shape of the belts. This has been carried 

 out in a very diff^erent manner from that 

 y used on their farm 

 tractor predeces- 

 sors. Instead of 

 being low and flat, 

 they are strung 

 out over frames 

 thirty to forty feet 

 long and from ten 

 to fifteen feet high, 

 depending upon 

 the size of the 

 tank. These 

 frames are armor- 

 ed with Harvey- 

 ized steel to pro- 



vide protection for the tank operators and 

 besides are curved up in the arc of a huge 

 circle at the front to give the vehicle its 

 wonderful tractive powers. This large 

 curvature acts as a huge wheel with a 

 tremendously long leverage equal to the 

 radius of the circle or the spoke of the 



All tanks have the common characteristic of being divided into three main compartments between the 

 two side caterpillar frames, the lookout, the ammunition, and the engine rooms. Part of the cater- 

 pillar tread of this machine was shot away, thus revealing the construction beneath the outer belt 



