Since this is posted in the WW1 forum im assuming military. You may have to obtain his military records to find out more, that is if the records have survived.
Unfortunately, more than half of their service records were destroyed in September 1940, when a German bombing raid struck the War Office repository in Arnside Street, London. However, an estimated 2.8 million service records survived the bombing or were reconstructed from the records of the Glossary - opens new windowMinistry of Pensions. This means that there is a roughly 40% chance of finding the service record of a soldier who was discharged at some time between 1914 and 1920.