Difficult to be sure but this seems the more likely of 2 possibles
1897 Feb 14 Born London. There are 2 William John Emmett born in London in the right quarter. The Navy record shows we want man born in Bethnal Green. There are some very mixedup/confused/bad Ancestry trees that have amalgams of 2 men with same name
1911 census at 23 Chilton Street, Bethnal Green
1916 Jun 27 Enlisted in Royal Navy
1919 Mar 1 Demobilised
1920 Sep 17. Joined RIC with RIC no 73119 & ADRIC no (803 ) . Wood Machinist and ex-soldier
1921 Jun 29 Posted to H Coy
1923 Married in Bethnal Green
1939 Register Ling at Dagenham, Printers Assistant, wife Lydia Elizabeth
1971 Oct/Dec died Havering , Essex