1916, STRENGTH AND FRONT.—
Begin with the FRONT and FIGHTING STRENGTH lines. The Strength line tells the Commander his actual numbers (by reference to scale 2), but he needs more. He looks at the line representing Front and marks the proportion it bears to Fighting Strength. Measure these lines in mid-June, 1916. Since January, FRONT (scale 1) has expanded by about one-fifth—from 67 to 90 miles. The Chart shows the reason. 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. Ground is won, but hardly and at great cost: the ascent of the Front line is slow.
PRISONERS.—
What are the enemy losses? How are his men fighting? The PRISONERS line (scale 5) tells best. Gradually the proportion of prisoners to (British) casualties increases: his casualties are growing, his resistance becoming less effective: the wearing-out process tells. Mark the concluding phases of the Somme battle. The PRISONERS line is nearer to that of casualties. The Tank has been introduced, and here is ocular evidence of its effectiveness. More tanks is one of the lessons of the lines.
1917, ARRAS.—
The Somme fighting ends. Again our armies are built up, until the 760,000 point is reached. FRONT, increased to nearly 120 miles by a relief of French troops, falls again to 105, owing to the German retirement about ARRAS. Heavy guns have increased from just over 300 to 1,500. Again our armies are ready, and the Battle of ARRAS opens the ALLIED SPRING OFFENSIVE. It is immediately effective, for casualties never reach the same height as in the Somme, and prisoners are much more numerous. The lines for the two battles show the difference vividly. But mark the big curve downward of the STRENGTH line. Casualties are now not so easily replaced.
MESSINES, YPRES, PASSCHENDAELE.—
Before STRENGTH is fully restored the Messines ridge is rent with mines (June 7th) and taken. July is devoted to preparation: STRENGTH reaches its zenith, guns still increase, and on July 31st the Battle of YPRES opens the great northern offensive. Fighting is bitter, and more costly than at Arras; CASUALTIES are at first high in relation to prisoners, but the PRISONERS line, as in the Somme, but more consistently, tends upward. The German is not "sticking" the terrible conditions and fierce fighting so well as the Britisher.