He received an emergency commission in the Rifle Brigade on 19 April 1941,[3] and was promoted war-substantive lieutenant on 1 October 1942 and temporary captain on 3 September 1943.
[5] In April 1945 Fiennes and his regiment, the 8th Battalion of the Rifle Brigade, were among the first troops to reach Bergen-Belsen concentration camp.
Tribich, who was 14 and ill with typhus when Bergen-Belsen was liberated, had previously survived the ghetto in her hometown and Ravensbrück concentration camp.
[6] After the war, Fiennes remained in the army, receiving promotion to war-substantive captain and temporary major on 15 January 1946.
[11] Fiennes was a trustee of the Ernest Cook Trust, which works for the preservation of English country houses and estates, from 1959 until 1995, serving as chairman from 1964 until 1990.