So far we have only found a William Brentnall on the census returns of 1891, 1901 and 1911. In 1891 he was 1 year old and lived with his parents in 117 Pendre Mold. His father was Samuel, a cobbler aged 66. His mother was Mary 37. His siblings were Matilda 14, Samuel 13 and sister Mabel Adeline 3.
Ten years later William was 11 and the family lived in Bro Celyn Mold. Mary was by now a widow, Samuel was 23 and a yardman on a farm. Mabel is listed as 11 years old which cannot be right.
In 1911 the family is in Bro Alyn, Lead Mills Mold. Mary was 58, Samuel 33, Mabel 23 and William was a 21 year old driver at a livery stables.
We have had no luck yet in finding anything to link him to the military.