In 1941, during World War II, the inhabitants of the island were evacuated to Arnstadt, Thuringia, later to Hertigswalde, near Sebnitz, Saxony.
In 1944, he volunteered to serve in the air force and was stationed in Ústí nad Labem, now in the Czech Republic, at the end of World War II.
In 1946, he published his first book, Der goldene Faden and then visited the college of education in Lüneburg, Lower Saxony.
In the same year, he moved to Reinbek, near Hamburg, and founded the magazine Helgoland, which was meant for inhabitants of the island, who had been expelled from it; it existed until 1956.
Inheriting a post-war literary desert, created by the Nazi Party's discouragement of creative writing for children in favour of a hoped-for return to true Germanic folk poetry, Krüss was a hugely important figure in the re-establishment of the freedom of imaginative story-telling.
His first children's book, The Lighthouse on Lobster Island (1956), was based on his own experience of growing up in Heligoland, and was followed by My Great-Grandfather and I (1959), a continuation in the same genre.