Before the breakdown of the March offensive "our guns had regained the upper hand," and in the later battles of the year the German artillery was finally mastered.
But immense as was the growth of the artillery factor, the ultimate problem was the old problem of co-operation and combination of _all factors_.

"Deep study of work other than one's own," "understanding of the other man's job"-- for the highest success in any branch of the Army, these were and are indispensable.

Only so can the vast machine work satisfactorily; only so can the human intelligence embodied in it come to its own.
To the two subsidiary services most in the public eye--tanks and aeroplanes--I will return presently.

As to the Signal Service, the "nervous system" of the Army, on which "co-operation and combination" depend, it has grown, says the Field Marshal, "almost out of recognition." At the outbreak of war it consisted of 2,400 officers and men; by the end of the war it had risen to 42,000.

Cables, telegrams, wireless, carrier-pigeons and dog messengers--every kind of device was used for keeping up the communications, which mean everything in battle.