[2] In 1939, reportedly after attending a performance of the symphonic poem Finlandia, he volunteered to fight on Finland's side in the Winter War.

Coincidentally, Kayser returned to Norway from Finland on this date, crying as he found the capital city Oslo invaded.

They were to parachute onto the Nevlandsheia plateau in Gjesdal and from there carry out a sabotage operation against the strategically important Sola Air Station in Western Norway.

[6] Kayser was one of the first two saboteurs to enter the Vemork facility on 27 February, crawling through a cable shaft, the other being the team leader, Joachim Rønneberg.

[10] For his role in the heavy water sabotage Kayser was awarded the Military Medal by King George VI of the United Kingdom.

[4] In the last year of the war the Norwegian resistance movement established base areas in remote locations in Norway to provide hiding places for people on the run from the German occupiers.

Five base areas were planned, although only two were completed (Bjørn and Elg) by the time of the German capitulation on V-E Day, with a third (Varg) still under construction.

In addition to serve as safe heavens the bases were also to train the refugees in guerilla tactics, using instructors from Norwegian Independent Company 1.

[12] Kayser had arrived in Masfjorden in October 1944 with a fellow Norwegian Independent Company 1 soldier, second lieutenant Severin Synnes.

The two had been transported to Masfjorden from the UK on the Royal Norwegian Navy submarine chaser HNoMS Vigra with orders to establish Bjørn West.

[3] On 8 May 2012, on the 67th anniversary of the end of the Second World War in Europe, a memorial to Fredrik Kayser was unveiled at Storetveit in Bergen.

Kayser left the military after the war, and spent the rest of his professional career working in the private business sector.