The voluntary organisations known as the British Red Cross and the St John’s Ambulance, together with the Quaker Friends Ambulance, carried out a great deal of valuable work in support of the army during the war.
If the person (male or female) served overseas, they will have qualified for campaign medals which can be researched in the normal way.
Unlike military records, details of service for men and women who served with these organisations are not held at the National Archives. The British Red Cross Society has an archive and provides a search service for Voluntary Aid Detachments and personnel records. Details can be seen at the British Red Cross Society website.