Norwegian War Medal Defence Medal 1940–1945 Order of the British Empire Distinguished Service Order Légion d'honneur Croix de Guerre Leif Hans Larsen Tronstad (27 March 1903 – 11 March 1945) was a Norwegian inorganic chemist, intelligence officer and military organizer.

After the invasion of Norway by Germany during World War II, 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.

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.

He then embarked on thirty months of professional practice in two local electricity companies, which was a requirement to enrol at Kristiania Technical School, a predecessor of the Faculty of Engineering at Oslo University College.

[2] He was ready to enroll at the Norwegian Institute of Technology, but waited one year, possibly wanting to strengthen his personal finances.

[3] He was an accomplished athlete and helped his hometown club Grane SK to two Norwegian 4 × 1500 metres relay records.

Tronstad had taken various stray jobs while studying,[3] and also finished his military service, reaching the rank of Second Lieutenant in the Norwegian Army Corps of Weaponry in 1927.

The work was completed in 1931 and his thesis, spanning 250 pages, was published in German as Optische Untersuchungen zur Frage der Passivität des Eisens und Stahls.

He was hired at the Norwegian Institute of Technology as a lecturer in the summer of 1931, although he spent the first year at the University of Cambridge, conducting further research with a scholarship from a memorial fund of Christian Michelsen.

[6] Following the death in 1934 of a professor of technical inorganic chemistry at the Norwegian Institute of Technology, Tronstad was appointed his successor on 17 April 1936, effective from 1 May.

In 1933, Leif Tronstad and Jomar Brun, the head of Norsk Hydro Rjukan, created a plan for industrial production of heavy water in Norway.

As Norsk Hydro were already producing ammonia for nitrogen fertilizer, Tronstad and Brun had realized that large amounts of electrolyzed water were available.

He brought his wife and children with him, but having no intention of taking them to a possible theatre of war, he left them in the Drivdalen valley.

Here, he helped organize volunteers from local rifle associations to form a line of defence meant to repel any advancing German forces.

One source of this information was Tronstad's old companion, Jomar Brun, still in charge of the plant,[7] who also helped people to flee the country by sea, via the Møre coast.

[8] He also maintained several contacts abroad, including scientists whom he knew from the Norwegian Institute of Technology: Harald Wergeland and Njål Hole.

He even wanted to enrol in active duty, but was stopped by the Norwegian military command, who considered him "too valuable" for the war theatre.

This had been established in December 1942 under the leadership of Colonel Bjarne Øen, and Tronstad was brought in as a reinforcement as the work burden increased.

[7] In the beginning, Tronstad had not been aware of the connection between heavy water and atomic weaponry,[8] but it eventually became clear that Germany could be running a nuclear energy project, especially after Harold Urey visited the United Kingdom in November 1941.

Brun would later communicate with England through Einar Skinnarland, a covert Special Operations Executive agent hailing from Rjukan.

He warned of the presence of civil housing, and argued that bombing was not even guaranteed to succeed, given that the heavy water facility was located in the armoured basement of the electrolyzing plant.

[8] The operation, codenamed Freshman, was a catastrophe, as all units except for one towing aircraft perished, either due to crash landings or in German captivity.

This resulted in the sinking of SF Hydro by Norwegian saboteurs, halting the heavy water transport, but again claiming many civilian lives.

[8] Concealed listening posts at Rjukan and Notodden also revealed high-level German discussions of long-range weaponry.

Fellow scientists Rideal and Evans later wrote that Tronstad "contributed directly to the speedy victory of the Allied Nations, besides saving the region which came to be known as 'Southern England' from an even longer and more severe ordeal than it actually endured".

On 11 March 1945, resistance member Jon Landsverk managed to travel with Torgeir Lognvik towards the mountains on the pretext of showing him some stolen goods.

However, on the same day, Torgeir's brother Johans became suspicious and decided to follow the ski trails, which led him to Syrebekkstølen.