Image copyright Getty Images

As many as 250,000 boys under the age of 18 served in the British Army during World War One. Fergal Keane remembers the sacrifice they made.

War confers many things on boys who pick up a weapon to fight. They learn the true meaning of fear. They test their own capacity for courage and the limits of human endurance, physical and mental.

Some find that killing comes easily to them, too easily. And others recoil from acts of blood.

But what unites all teenage warriors is the speed with which they are hurled into a place of maiming and death.

Describing the training of a boy soldier in World War One, Wilfred Owen, wrote in Arms and the Boy:

Let the boy try along this bayonet-blade

How cold steel is, and keen with hunger of blood;

Blue with all malice, like a madman's flash;

And thinly drawn with famishing for flesh.

Lend him to stroke these blind, blunt bullet-heads

Which long to muzzle in the hearts of lads.

Or give him cartridges of fine zinc teeth,

Sharp with the sharpness of grief and death.

From Homer's Iliad to the present day the stories of boy soldiers evoke a particular sadness, resonant as they are of the destruction of youth and possibility.

But at the outbreak of the Great War there was nothing to suggest that the tens of thousands of boy volunteers were about to join a long, doomed procession.

Nearly 250,000 teenagers would join the call to fight. The motives varied and often overlapped - many were gripped by patriotic fervour, sought escape from grim conditions at home or wanted adventure.

Image copyright Other Image caption After being wounded on the battlefield it took Cyril Jose two days to crawl back to the British lines

Technically the boys had to be 19 to fight but the law did not prevent 14-year-olds and upwards from joining in droves. They responded to the Army's desperate need for troops and recruiting sergeants were often less than scrupulous.

"It was obvious they weren't 19," says historian Richard Van Emden, "but you'd have a queue of men going down the road, you're getting a bounty for every one who joins up, are you really going to argue the toss with a young lad who's enthusiastic, who's keen as mustard to go, who looks maybe pretty fit, pretty well. Let's take him."

Fifteen-year-old Cyril Jose was a tin-miner's son from Cornwall. With the region suffering from heavy unemployment, the boy with a strong sense of adventure joined up. From his training camp he wrote an excited letter to his sister:

"Dearest Ivy, stand back. I've got my own rifle and bayonet. The bayonet's about 2ft long from hilt to end of point. Must feel a bit rummy to run into one of them in a charge. Not 'arf. Goodbye and God bless you, from your fit brother, Cyril."

Cyril survived the war but the bloodshed he witnessed in France turned him into a vehement opponent of militarism for the rest of his life. In one letter home he poured scorn on the British commander, Field Marshal Earl Haig.

"What brains Earl Douglas must have. Made me laugh when I read his dispatch. 'I attacked.' Old women in England picturing Sir Doug in front of the British waves brandishing his sword at Johnny in the trenches... attack Johnny from 100 miles back. I'll get a job like that in the next war."

Why did so many teenagers make it to the battlefield?

Image copyright Getty Images

Recruitment officers were paid two shillings and sixpence for each new army recruit, and would often ignore any concerns they had about age.

Many people at the start of the 20th Century didn't have birth certificates, so it was easy to lie about how old you were.

The minimum height requirement was 5ft 3in (1.60m), with a minimum chest size of 34in (0.86m). If you met these criteria you were likely to be recruited.

Some young boys were scared of being called a coward and could not resist the pressure from society.

How did Britain let 250,000 under-age soldiers fight in WW1?

The patriotic imperative at the outbreak of war was not confined to British-born boys. For the children of migrants, rallying to the flag was proof of loyalty to their new country.

Aby Bevistein was born in Russian-occupied Poland in 1898 and came to London when he was three. In September 1914 Aby volunteered, changing his surname to the English "Harris".

Image copyright other Image caption Aby Bevistein's parents were heartbroken when he joined the army

Soon after his arrival in France Aby discovered the wretched nature of trench warfare. He wrote home:

"Dear mother, I've been in the trenches four times and come out safe. We're down the trenches for six days and then we get relieved for six days' rest. Dear mother, I do not like the trenches. We're going in again this week."

For Aby, and many like him, the trenches meant cold and mud, wet clothes and rats, the smell of death and the sight of mutilated flesh, long monotonous hours interrupted by terror.

On 29 December 1915 Aby was caught in a German mine explosion - the enemy had tunnelled under the trench where he was stationed. He was wounded and suffered what was then simply called "shock". In today's military lexicon it would be described as "combat stress" or "post traumatic stress disorder".

By early spring Aby was back on the front. On 12 Feb 1916 the Germans again attacked his position, this time with grenades.

Dear mother, I'm in the trenches and I was ill so I went out, and they took me to the prison and I'm in a bit of trouble now Aby Bevistein

Suffering from shock, Aby wandered back and forth along the British lines. He was eventually arrested and charged with desertion. His last letter home is that of a boy who seems determined to underplay his situation, not to put stress on his mother at home.

"Dear mother, I'm in the trenches and I was ill so I went out, and they took me to the prison and I'm in a bit of trouble now."

The following month Aby then aged 17, became one of the 306 British soldiers executed during the Great War.

Those who survived the trenches and came home brought memories that retained the power to haunt until the end of their lives. St John Battersby was 16 when he was severely wounded at the Battle of the Somme in July 1916.

Like all of the teenaged officers, Lieutenant St John Battersby had responsibilities far beyond his years, as his son, Anthony, recalls:

Image copyright other Image caption St John Battersby was first stationed near Serre in the Somme region

"There's my dad, 16-years-old, really in the war. He is responsible for 30-odd men and his decisions may result in them dying or not dying. This was it."

Three months after he was wounded, St John Battersby was back in France leading men in battle again. He could have opted to stay at home - by now the government was taking all those under 19 years of age out of the front lines. But a shortage of experienced officers meant they were allowing boys like St John Battersby to stay on if they wished.

A sense of duty compelled St John to return. Soon after coming back he was blown up by a German shell and lost his left leg. Determined to continue helping the war effort, he asked for, and was given, an administrative job in Britain.

But years later, after a fruitful life serving as a country vicar, the memories of war returned. His son Anthony remembered his father's last hours.

"In the hour or two before he died, he was on the Western Front, yelling, 'the Bosch are coming. We're going over the top now'. Right down deep on the ground floor of his memory was the Western Front."

The man facing death was once again the boy who had cheated it so many times.

Teenage Tommies will be broadcast on Tuesday 11 November at 21:00 GMT on BBC Two. Or catch up later on BBC iPlayer.

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