At the rank of ensign and only 22 years of age Rønneberg headed the
commando raid codenamed 'Gunnerside' which flew from it's training camp
in Scotland, and parachuted over Nazi-occupied Norway during World War
II. There he re-grouped with another team of waiting Norwegian
commandoes - codename 'Grouse' - and together they blew up the Heavy
Water plant at Vemork, Telemark, helping to end Hitler's quest for the
atomic bomb. The act was later referred to by the British SOE (Special
Operations Executive) as the single most important act of sabotage
during the entire war. Towards the end of the war Rønneberg would also
lead 'Operation Fieldfare' in the Tafjord Mountains of Norway. After
the war he among other things worked at Norwegian National Broadcasting
(NRK) as a secretary of programming. Later retired to live in Ålesund,
Norway.