With the code name John, Nielsen led other resistance fighters of the Holger Danske against the Nazis.
[3] Nielsen considered careers in agriculture and shipping over two and a half years and then studied at Ranum seminar to become a teacher.
[2] Next, Nielsen taught mathematics at a school in Skovshoved (on the Øresund coast north of Copenhagen, Denmark).
[4] Nielson knew Jens Lillelund, the sole fighter of the Forum Copenhagen action that remained in Denmark, and the rest fled to Sweden across the Øresund.
[5] The SOE supported the resistance movement in occupied countries during World War II.
[7] The organization sabotaged places to gain weapons and supplies, to damage factories,[4] and to disable railway lines and bridges that transported soldiers and equipment.
[6] With Citron and Flame, Jørgen Haagen Schmith and Bent Faurschou Hviid Nielsen picked up weapons that were illegal in Denmark that the Royal Air Force sent.
The British intelligence service wanted the device to use in tandem with a radar system for airplane pilots to help them navigate during dangerous night flights over Germany.
Most of the remaining HD2 fighters went to Sweden, except Hviid, which curtailed their sabotage in February 1944, but there was a greater focus on eliminating the informers.
[11] Svend Otto Nielsen told Jens Lillelund his feelings about working underground while at the apartment of Hedvig Delbo, who was later found to be the Gestapo operative who informed on him, I hope I survive the war.
I don't think you'll get through, but it's just possible I might... [12]Hedvig Delbo, a Norwegian dressmaker, informed the Gestapo about Nielson for 20,000 Danish kroner.
[13] Nielsen and Jens Lillelund (Finsen) arrived at Delbo's apartment on 6 December 1943 for lodging.
[2] In the morning, the Gestapo came for Nielsen and Jens Lillelund (Finsen) after they left Delbo's apartment.
Delbo lived and escaped to Norway but later returned to Copenhagen and operated a dressmaking shop under an assumed name.
[17] The most notable attacks made by HD were to a steel mill in Jutland and the B&W shipbuilding yard in Copenhagen,[6] which were conducted in retribution for Nielsen's arrest and treatment.
Nielsen was unable to move out of bed due to his broken leg, and he was in a poor state.