Nobel prize-winning German author Guenther Grass has admitted in his new book "Beim Haeuten der Zwiebel" ('Peeling the Onion') that he served in the Waffen-SS, the combat arm of the Nazi paramilitary group headed by SS chief Heinrich Himmler. Danzig-born Grass, 78, said he volunteered for U-Boot service toward the end of the Second World War but was called up instead to serve in the Waffen-SS in the eastern city of Dresden. The author, best known for his first novel "The Tin Drum" and an active supporter of Germany's Social Democratic Party (SPD), said the secret had been weighing on his mind and was one of the reasons he wrote the book of recollections which details his war service. Due to the publicity driven by the scandal around the admission, booksellers put the book out earlier than planned on Wednesday (August 16). "Since we have put it out in the store, since 10 o'clock this morning there have permanently been people buying it or customers stopping and looking at it. There is a lot of interest in the book," said Bianca Kraemer the spokeswoman for the book store Duessmann in Berlin. "It does make me think, but nevertheless Guenther Grass is one of the most important authors in the world. In brief, such people as Guenther Grass as authors have helped to form Germany as it is today, that such a strong democracy as Germany was able to develop, we certainly have people like Guenther Grass to thank for that," said Heye Osterwald as he bought the book. "I would have bought the book anyway, because I am a big fan of Grass, and I have read everything of his, so I didn't buy it because of that, but I do have to say that the publicity made me aware of it. I would like to know his side of the story," said Bill Niven. Grass was wounded in 1945 and sent to an American prisoner of war camp and later became a prominent peace activist. He said he had volunteered for army service as a way of breaking away from home and family. One of the most powerful organisations in Nazi Germany, the SS played a key role in the Holocaust, establishing and operating the death camps in which millions died. The Waffen-SS grew into a force of 38 combat divisions with almost one million men and it was condemned as part of a criminal organisation at the post-war Nuremberg trials. Grass has received many awards throughout his career, winning the Nobel Price for Literature in 1999. He is seen as part of the artistic movement known in German as "Vergangenheitsbewaeltigung" or "coming to terms with the past". Grass opposed the reunification of Germany in 1990, arguing that the country would be in danger of reverting to its role as a war-mongerer.