Not that it makes much difference to the question of what to do about Syria, but most historians agree that Hitler deliberately refrained from using chemical weapons.
This Stanford professor (a computer scientist and technology historian) says the Nazis never used poison gas on the battlefield. The infallible Wikipedia says they may have done so once, to end a three-month siege of Soviet troops. This article says Hitler wanted to use them, but a Nazi scientist persuaded them not to, by exaggerating the threat of Allied retaliation. And here’s a book that says neither side used chemical weapons in WWII because both feared a massive retaliation, possibly against civilians.
Again, this does not affect Kerry’s and Obama’s case for bombing, but in the future it might work better to say “Not even Hitler . . .”