bullet

     In WW2, German military create new formation.  It is "bullet".  The shape is like arrow mark.  The creator is Heinz Wilhelm Guderian who is German general. 
     "bullet" aim attacking enemy headquarter.  Image the boxing.  If you was punched your head,  you will collapse on the floor by the concussion.   punch is "bullet", head is enemy headquarter, concussion is shock caused by our attack. 
     Soldiers obey an orders,  but if they are not gave an order, they never done anything.   that is to say,  atacking enemy headquater lead us win.
     Tip of arrow is tanks. Middle stick is other tank or truck.   Sticks growed from tip are truck loaded with infantry.
1)Cannon or dive bomber attacks enemy to be weaking.(So conducter must catch command of air.)
2)Tanks devastate weaking enemy.  Their mission is to hole in the enemy defense.
3)Track fulled with infantry defense enemy counterattack or expand the hole to through more friends.
4)Finally,  the first tanks attack enemy headquater.

German Military beated France Military , Yugoslavia Military, Poland Military in WW2 and defeat Soviet in the operation of Barbarossa.
Battle using "bullet" is called "lightning war".  Now US also adopted this formation.
He is Heinz Wilhelm Guderian.Sorry I could not find picture of "bullet".

Heinz Wilhelm Guderian

circle

    When soldiers rest, they form the formation which called "circle".  In US this is called "assembly".  I maight say that formation's weakpoint is corner.  In case of circle, as you know, there is no corner.  So if soldires were attacked, the damege would be minimum. 
     Basically, when we don't know what is enemy's target or object, "circle" is also formed.

"Circle" has been used by every Militaly.
This formation is too small. But "circle" is like this picture.