Feature: Britain remembers bloodiest day in military history as dead of the Somme mourned

The dawn chorus of singing birds was shattered Friday as the shrills of whistles echoed across towns and villages in Britain.

The whistles were blown at exactly the moment 100 years ago when thousands of troops were given the signal to embark on what became the Battle of the Somme.

The soldiers, many of them teenagers, old enough to fight for the country but too young to vote, were sent to their deaths with an order to go "over the top". It meant leaving their relative safety of the trenches that had been dug to attack enemy lines in northern France.

Many had written final messages to their families and loved ones at home as they awaited that shrill of the whistle.

Within a matter of hours almost 20,000 British troops lay dead, a further 40,000 injured, a toll never since exceeded in warfare.

The slaughter happened because the better equipped German soldiers had machine guns, able to dispatch bullets at the rate of 100 rounds a minute.

Across Britain there was a two minute silence as an act of remembrance, ended by the blowing of those whistles, sounded just like they were on that July 1 morning in 1916.

Overnight young soldiers, many the same age as those cut down in the Somme, solemnly provided a guard of honor at war memorials across the nation.

Throughout Friday solemn events were taking place in both Britain and France to commemorate the centenary of a battle that would forever change the way future battles would be fought.

In a message Friday British Prime Minister David Cameron paid tribute to the fallen soldiers.

He said: "Today is a chance to reflect on the sacrifice not just of the thousands of British and Commonwealth troops who gave their lives, but of the men on all sides who did not return home. It is an opportunity to think about the impact of the devastation felt by communities across all of the nations involved, which left mothers without sons, wives without husbands and children without fathers."

On Thursday night Queen Elizabeth attended a special service of commemoration at Westminster Abbey in London. There she placed flowers on the grave of the unknown soldier. The tomb holds an unidentified British soldier killed on one of the battlefields, brought back and buried in the abbey to honor the unknown dead of the war.

The Battle of the Somme was fought along a front just 24 km long, close to the banks of the River Somme. On that first day the British had advanced just five square kilometres, and after 141 days of fighting had advanced just over 11 kilometers. Endit