A regional newspaper in Germany has claimed Grass was pre-empting the release of the information about his SS history from the secret police archive next year.
The newspaper, Kolner Stadtanzeiger, said the information was contained in Nazi era records compiled by the Stasi, the secret police of the communist government of former East Germany.
The Waffen SS was the combat arm of Adolf Hitler's notorious elite force, which expanded to nearly one million members during the war.
There's also Salman Rushdie and John Irving defending him. Incidentally, I didn't know Ezra Pound was a Nazi sympathiser.
Anyhow, yesterday in the comments, one of the reoccurring questions was why he decided to reveal it now. Why not years ago? Was it nothing but a crass marketing ploy, because that seems to have worked as well. His memoirs have gone on sale two weeks early due to interest.
There's a bit more here about his service:
It turns out that Guenter Grass was a trooper in the SS Frundsberg Division, which fought against the Allies in Normandy and at Arnhem, and later against the Soviet army in Pomerania and Saxony.
Grass himself claims he never fired any shots and was a poor soldier.
It has to be said, that up to now, the Frunsberg Division has not been implicated in any major atrocities or war crimes - even though the SS as a whole was classified as a criminal organisation after the war.
Grass's own lack of candour about his past can be seen as an ironic commentary on his own insistence that Germans need to make an honest appraisal of their own horrible past.
For many, his status as a moral authority will have been compromised for good.
And his opinion, at the time of being moved to the unit, which is somewhat contradictory I feel in how he portrays himself as a poor soldier:
Few details of the author's service were given other than that he had served in the Waffen SS Frundsberg Panzer Division after failing to get a posting in the submarine service.
The SS, which began as a private bodyguard for Nazi leader Adolf Hitler, grew into a force nearly one million strong and both acted as an elite fighting force and ran death camps in which millions of people were murdered.
The Waffen SS was the combat section of the organization and extended to 38 divisions. It was declared part of a criminal organisation at the Nuremberg Nazi trials after the war.
"At the time" he had not felt ashamed to be a member, he said but he added: "Later this feeling of shame burdened me."
"For me... the Waffen SS was nothing frightful but rather an elite unit that they sent where things were hot and which, as people said about it, had the heaviest losses," he said.
"It happened as it did to many of my age. We were in the labour service and all at once, a year later, the call-up notice lay on the table. And only when I got to Dresden did I learn it was the Waffen SS."
All articles are from that handy news source of the BBC. I can't be arsed going off to find other media outlets, and the BBC had a nice link bar for it.