World War One broke out on 28 July, 1914. Fifty years later, one of the German soldiers, Stefan Westmann, told the BBC about his experiences fighting in the conflict.

Warning: The following article, and video clip, contain graphic descriptions that some readers and viewers might find upsetting.

World War One broke out on 28 July 1914. To mark its 50th anniversary in 1964, the BBC made The Great War, an ambitious history of the cataclysmic conflict. One of the 280 eyewitness interviewees was a German soldier who gave a harrowing and unforgettable account of what it feels like to be forced to kill.

Stefan Westmann was a medical student who before the war had barely even used a scalpel. A few months later, Westmann and his German comrades were on a battlefield attacking a French position when he came eyeball-to-eyeball with an enemy soldier. Both clutched their bayonets in dread of what must happen next.

"For a moment I felt the fear of death, and in a fraction of a second I realised that he was after my life exactly as I was after his," he said.

"I was quicker than he was. I tossed his rifle away and I ran my bayonet through his chest. He fell, put his hand on the place where I had hit him, and then… he died. I felt physically ill. I nearly vomited. My knees were shaking, and I was quite frankly ashamed of myself."

In 1964, by then a grandfather with a distinguished medical career behind him, Westmann was transported back in his mind to that field in France to relive a trauma that remained raw.

Before the war, Westmann had been studying medicine in Berlin. While his fellow soldiers also had unremarkable backgrounds – "ordinary people who never would have sought to do any harm to anyone" – he said they had not seemed disturbed by the violence they had inflicted.

"How did it come about that they were so cruel?" he said. "I remembered then that we were told that the good soldier kills without thinking of his adversary as a human being. The very moment he sees in him a fellow man, he is not a good soldier anymore."

Westmann said he had wished the dead French soldier could have raised his hand and........

© BBC