Question

why does the army tank rest upon a continuous chain

Answer 1

The army tank rest upon a continuous chain as these tanks are very heavy weighted and they cannot have tires as,they have to fire a huge and long projectile...to very far away distances.....so Chains are there to help them as they have the ability to balance them in any field ...Chains help them to run on sandy,rocky or Swampy areas whereas tires do not do this/......

Answer 2

Tanks are very heavy and they cannot rest on rubber tires.  We could use steel tires.  But the small area of contact between the ground and the tires creates a high stress (pressure) on the ground.  Then soft or Earthen ground or loose roads will sink.  It affects the mobility of tanks which move at 40 kmph or more.

Hence a steel chain is used.  It is called continuous track or caterpillar track system. The chain or band is made of modular steel plates.  These allow distribution of the weight over a very large area.  So tanks move continuously with out problems.  

These metal plates help movement of tanks in any kind of terrain with uneven surface.  It can climb heights, abrupt steps which is very difficult for tires or steel wheels.  It gives grater control for turning, slowing or speeding up in deserts, among mountains, on damp lands, on roads etc.

Further when missiles are fired, the recoil force is transmitted to the ground.  Hence, the continuous track helps in distribution of force over large area.