But meanwhile _Fighting Strength_, then the vital factor for attack, has risen from 470,000 to 680,000, nearly one-half.

The Army has been built up by new Divisions for the great Somme offensive.
CASUALTIES .-- The battle opens.

The red line of casualties leaps into prominence and, with its ascent, STRENGTH falls.

Reinforcements are needed.

They arrive to replace casualties, and STRENGTH goes up again.
So through the long conflict these lines act and react.