[3][4] At the age of 18, Danielsen moved to Scotland to train as a marine engineer, later working on voyages to South Africa and the United States.

[3][4] After responding to a job posting in South Africa, Danielsen worked for the Congo-Balolo Mission in the Congo Free State from 1901 to 1903, primarily in Bonginda.

As it was, we sprang a leak coming down the river on 13th September and apart from other consideration, I do not think it would have been possible to have the vessel continue running much longer.

"[1] Danielsen refused any compensation for his work, and Casement instead asked his superior to authorise him to make a donation to the Congo-Balolo Mission.

Following the report's conclusion, he exhibited the photographs in meetings in England and the Faroe Islands, playing a part in galvanising the effort against Leopold II's ownership of the Congo.