WO 339/66132 TNA indicates that Dennis William and William are the same man
1883 Jun 22. Born Waterloo, Lancs, the illegitimate son of Martha Knight. She married John Blackhurst in 1885. The only birth in that area with "Dennis William" has surname "Allsop", which I think is him as there are no other references in the records to this man.
1891 census - I cannot find them.
1901 census at 19, Ruthven Road, Litherland, Lancs
1914 Dec 23. Married in Devon to Gertrude Charlotte Dunnett. Occupation "Sergeant of Royal Garrison Artillery"
1915 Dec 9. Landed in France.
1916 Jun 17. Commissioned 2nd Lt
1921 Jul 6. Joined ADRIC with service no 2109. Posted to M Coy
1922 Jan 19. Discharged at demobilisation of ADRIC
1939 Register. Living with Gertrude C Knight at 1 The Cross Lane , Frimley and Camberley U.D., Surrey. He works for RMC Sandhurst
1942 Jul 25 Died in explosives accident
WO 339/66132 TNA indicates that Dennis William and William are the same man