The two main lessons learnt were: firstly, that speed and circuit are the two essentials for an open-warfare machine; and secondly, one which has already been mentioned but which is so important that it is worth mentioning again, namely, that no great Army, such as the Germans massed against us on March 21, can depend on road and rail supply only. Consequently unless these means of supply are supplemented by cross-country mechanical transport, that is, transport which is independent of road and rail, the greatest success will always be limited by the endurance of the horses’ legs. Men without supplies are an incumbrance, and guns and machine guns without ammunition are mere scrap iron. Had the Germans after March 26 been able to supply their troops mechanically across country, there can be little doubt that their advance would have been continued, for we could not have stopped it, and they might well have won the war. Fatigue may stop an advance gradually, but lack of supplies will stop it absolutely--this is the second and greatest lesson of the Second Battle of the Somme, if not of the entire war.
In battle, co-operation between the commander and his troops, and between the troops themselves, depends very largely on the efficiency of the signal organisation. In a formation such as the Tank Corps, the chief duty of which was close co-operation with the infantry, the necessity for a simple though efficient communication was fully realised by Colonel Swinton as far back as February 1916, when he wrote his tactical instructions for the use of tanks, extracts from which have been given in Chapter IV. Though time for instruction was limited, special wireless apparatus was prepared and men trained in its use, but as orders were received not to equip the tanks with this apparatus they were dispatched to France in August 1916 without it.
On September 11 the first instructions relative to tank signals were published with the Fourth Army operation orders; they read as follows:
Red flag Out of action. Green flag Am on objective. Other flags Are inter-tank signals.
Series of T’s Out of Action. Series of H’s Am on objective.
A proportion of the tanks will carry pigeons.”
The use made of these signals is not recorded, and no time was available, until after operations were concluded in November, wherein to organise more efficient methods.