William Horsler was the eldest son of George and Ann Horsler of Great Bramingham, who had seven sons serving on the Western Front. Three brothers were killed and two, including William, were wounded.

William had twelve years service in the 8th Hussars in India prior to WWI and was working as a postman at Ampthill when he was called up from the Reserve to serve in the Military Police. He went to France in July 1915. Whilst off-duty he went up to the frontline to gather information about a missing brother, Walter, and was wounded in the neck and shoulders. He was invalided out and returned to his employment with the post office.