Bass's acting career began at Unity Theatre, London in the late 1930s, appearing in Plant in the Sun alongside Paul Robeson, and as the pantomime King in Babes In the Wood. After the outbreak of the Second World War, Bass joined the Middlesex Regiment as a despatch rider. Despite being kept busy with his duties, he found time to become involved in concert parties, as well as taking part in documentaries for the Army Film Unit.