The first action involving the British in the First World War was a cavalry skirmish - German lances against British swords. But, within eight weeks, any hopes for a swift end to the war were dashed when it was transformed into a bloody trench stalemate that would last for three years.
Why did the whole nature of warfare change so dramatically during this one brief period? Timewatch investigates.

See Peacemakers, showing tonight at 10pm on BBC4