I am researching Henry O'NEILL or O'NEIL (born 1883 in Oldham, UK but grew up in Bolton, UK). I have very little information on him but do happen to know that he was a sapper in the Royal Engineers. His marriage certificate gives his number as 341541 (although it is hard to read) then there are two illegible words and 'Machinist'.
Could anyone please advise of how I could go about researching him using this information.
Thanks in advance