The Allies got ready for the attack by starting a massive artillery bombardment that lasted a week and used more than 1.75 million shells to try to destroy enemy positions and cut the barbed wire that protected German trench defenses.

On the morning of July 1, many of the British 4th Army's volunteer soldiers were making their first appearance in a major fight. They advanced on a 15-mile front north of the Somme River. Meanwhile, five French divisions pushed along a front of eight miles to the south, where the German defenses were weaker.

The leaders of the Allies thought that the bombardment would weaken the Germans' defenses so much that their troops would be able to move in without being stopped. Many German defenses were deep underground trenches. They were stronger than expected, and barbed wire was still in place in many places.

Thousands of invading British troops, many of whom were stuck in "no man's land" between the two sides, were killed by German machine gun and rifle fire along the front.

At the end of the first day, 19,240 British soldiers had been killed and over 38,000 had been hurt. This was almost as many deaths as the Allies had in May and June 1940 when they were defeated in the Battle of France. 

Towards the south, other British and French forces saw some success, though their gains were small in comparison to the horrific losses experienced on that first day of fighting.

Nevertheless, Field Marshal Douglas Haig of Britain was adamant that the offensive continue, and so over the course of the next two weeks, the British launched a series of smaller attacks on the German line, increasing the pressure on the Germans and eventually forcing them to redirect some of their resources away from the Battle of Verdun.

On the morning of July 15, the Brits opened fire with artillery and then launched a huge assault on Bazentin Ridge in the northern part of the Somme. The Germans were caught off guard by the attack, and the Brits were able to push forward and take the settlement of Longueval.

In this lengthy and bloody war of attrition, the Germans had lost 160,000 soldiers by the end of July, while the British and French had lost over 200,000.

German General Erich von Falkenhayn was replaced by Paul von Hindenburg and Erich Ludendorff by the end of August, when morale plummeted as a result of setbacks at the Somme and Verdun. After a change in leadership, the Germans altered their strategy and began constructing a new defensive line behind the Somme front, which meant they lost ground but inflicted more fatalities on the advancing Allies.

British fire barraged Flers Courcelette on September 15, followed by an advance of 12 divisions of infantry and 48 Mark I tanks.

Yet, as the tanks were still in their infancy, several of them malfunctioned before reaching the front lines. Although the Brits were successful in pushing forward by about 1.5 miles, they suffered over 29,000 losses and ultimately failed to achieve a decisive breakthrough.

Another Allied effort was thwarted in the first days of October due to terrible weather and the difficulty of crossing muddy terrain while under heavy fire from German artillery and fighter planes. After months of fighting, the Allies finally broke through to the German defenses in the Ancre River valley in the middle of November.

True winter weather arrived on the Somme on November 18, prompting Haig to call off the offensive and effectively ending the brutal struggle of attrition there until the following year. In spite of fighting for 141 days, the British had made only a seven-mile advance and had not succeeded in breaking the German line.

The opening day of the Battle of the Somme, in particular, would come to symbolize the terrible and senseless deaths that characterized trench combat during World War I. It would be easy to blame British officers, especially Haig, for not calling off the offensive after suffering such heavy casualties. In 1914 and 1915, many British men volunteered for military service, and the Somme was the first time many of them faced enemy fighting. Many served in "pal battalions," or groups composed of people from the same town or neighborhood. Over 720 soldiers from the 11th East Lancashire battalion (often called the Accrington Pals) fought on July 1 at the Somme, and 584 of them were killed or injured, leaving their village devastated.

After losing a lot of men in the Battle of the Somme to the Allies, the Germans decided in March 1917 that it would be smarter to retreat to the Hindenburg Line than to keep fighting over the same land for the next few months.

There is considerable disagreement over the actual numbers, but by the end of the Battle of the Somme, the Germans had lost more men than the British had won. Those British forces that had made it through the war had also learned a lot that would prove useful in the long run.