A breach was made south of the Somme, but the marshes prevented development, while to the north, the offensive was held on the Ancre lines.
Putting to profit the German failure at Verdun, where the enemy masses, after appalling sacrifice of human life, gradually became blocked in a narrow sector (7½ miles in width), the Allies widened their front of attack.
After an effective "pounding" by the guns which annihilated all obstacles to a considerable depth, the assaulting waves went forward simultaneously along a 24-mile front, feeling for a weak sector where a breach could be made. The attack was a complete success in the diversion sector, south of the Somme, thanks to the nature of the ground, but, as previously stated, it was not possible to follow it up immediately.
North of the Somme the British offensive was held.
Warned by the immense preparations, the Germans were not taken unawares. Their reserves flowed in and resisted on new defensive positions. The advance of the French 6th Army was slowed down to correspond with that of the British.
The Battle of Attrition
(See the sketch-maps on pages [13], [18], [27].)
This attempted break-through (July 1-12) soon changed into a battle of attrition (July 14, 1916, to March, 1917).
The Allies' plan now was gradually to shatter the German resistance by a continuous push along the whole line, and by vigorous action at the various strong-points.
The gains of ground diminished, but the German reserves were gradually used up. In spite of their hastily constructed system of new defences, the Germans realised the precarious nature of their new lines, and were forced, in March, 1917, to fall back and shorten their front.