Leif Hans Larsen Tronstad DSO, OBE (27 March 1903 – 11 March 1945) was a Norwegian scientist, intelligence officer and military organizer.
He graduated from the Norwegian Institute of Technology in 1927 and was a prolific researcher and writer of academic publications.
A professor of chemistry at the Norwegian Institute of Technology from 1936, he was also among the pioneers of heavy water research, and was instrumental when a heavy water plant was built at Vemork.
During World War II Norway was invaded by Germany and Tronstad conducted domestic resistance for one year before fleeing the country for England.
There, he gathered valuable intelligence from Norwegian sources, both on the development of the V-2 rocket and the growing German interest in heavy water.
In 1943 Tronstad planned Operation Gunnerside, in which the German access to heavy water processing at Vemork was severely impeded.
His information about the V-2 rocket contributed to the massive Allied bombing of Peenemünde.
For a long time Tronstad had wanted to return to Norway to organize resistance work, however he was prevented by the Norwegian military authorities in Britain.
In 1944, however, he did travel to Norway, to organize Operation Sunshine, for the defence of Norwegian infrastructure.
After five months in the country, he was killed in action after his team had taken the local bailiff hostage.