Edward Snowden, who had access to basically all the US governments secrets for NSA and CIA with the highest above top-secret clearance, went specifically looking for stuff related to this and says that he came up with nothing. Out of anyone who could know things about this, I find his situation and argument to be most convincing.
Perhaps, but there's all kinds of tangentially-related stuff that could have been leaked but wasn't. Nor was mentioned by Snowden. One already-public example being the 2004 Nimitz incident, which is of genuine national security concern.
I know Snowden is highly-revered around here, but he's not all-knowing, and I'm fairly certain he did not have access to the entire US IC store of intel.
