During WW2 Niven was with the 7th Anti-Tank Regiment. On 27th November 1941 he played a key role in the unsuccessful attempt to defend the 5th Brigade Headquarters of Brigadier Hargest at Sidi Azeiz in the Libyan desert. Taken prisoner he escaped on several occasions and suffered at the hands of the Gestapo. His actions on 27th November 1941 are recounted in two of the WW2 official histories, 2nd New Zealand Division Artillery and The Relief of Tobruk.

At end of war Michael Niven returned to New Zealand, living initially in Auckland. At this time he had an extreme phobia about the Gestapo and he would sit on the stairs of his landlady’s house with a loaded rifle waiting for the Germans to come. It was in response to this that his landlady gave him the Webley revolver - presumably because it was less visible than the rifle.

Michael Niven later returned to Wellington where he practised as a vet for a number of years before deciding to return to England in the early 1950s. At this point he gave the revolver to Mr Hursthouse. Niven and Hursthouse had been friends before the war, both attending Victoria University circa 1935, and had resumed their friendship when Michael Niven returned to Wellington.