I was looking at your grandfather, William Devlin's WWI British Army Service Records on Ancestry.com. It appears that he joined the 18th Hussars in 1911, but he kept getting into trouble due to his misconduct, and was finally discharged in 1914. There are lots of pages for William, and one includes a letter to the government from his mother, Mrs. M Hold, in 1915, in which she says she has not heard from William and asks if he has been killed overseas. He got into the Royal Field Artillery, but was discharge in 1916 for misconduct. He was called up for WWI in November of 1917, at which time he was living with his mother Mrs. M. Luthwaite at 50 Bridge Street West in Middlesbrough. He requested to go into the Royal Field Artillery as a gunner. He went AWOL a couple of times in 1918, and was discharded in October of 1918. There is severals pages of information, one of which lists his mother Martha, and his brothers James, Robert, Thomas and Charles (same group as in the 1911 census). His number appears to be 55466 with the RFA and 7961 with the Hussars, and he writes a letter in 1918 from a hospital asking he he can wear a ribbon (1914 Star). If you do not have an Ancestry.com subscription, and if you don't have copies of all these papers, see if your local library or LDS family history center has an Ancestry.com subscription that you can access. Enter William's name and 1888 birth year. When the first page comes up, there are more pages infront of it, and after it. If this compares with information that you already have, then this paperwork could link your grandfather William to parents John Devlin and Martha Sweeting Devlin Hold Luthwaite Carter.