This isn't just a gaffe but rather a serious breach of security.

Remember that "secret bunker" where Dick Cheney would go when it was necessary to protect the line of succession by assuring the survival of the Vice President if something were to happen to Bush? We know from

Ever wonder about that secure, undisclosed location where Dick Cheney secreted himself after the 9/11 attacks? Joe Biden reveals the bunker-like room is at the Naval Observatory in Washington, where Cheney lived for eight years and which is now home to Biden. The veep related the story to his head-table dinner mates when he filled in for President Obama at the Gridiron Club earlier this year. He said the young naval officer giving him a tour of the residence showed him the hideaway, which is behind a massive steel door secured by an elaborate lock with a narrow connecting hallway lined with shelves filled with communications equipment. The officer explained that when Cheney was in lock down, this was where his most trusted aides were stationed, an image that Biden conveyed in a way that suggested we shouldn't be surprised that the policies that emerged were off the wall. 

points out that this particular bunker probably protected the Veep's aides. He adds:

Even so, what was this moron doing musing about vice-presidential security in front of an audience, even one that's supposedly "off the record" as the Gridiron's is? Stephen Hayes notes at the Standard that he visited Cheney's home more than a dozen times and reported extensively on security precautions and yet not until Biden blabbed did he learn that there's a secret facility at the Observatory. I googled around to try to debunk his claim that this was, in fact, classified information, but the only evidence I can find that the bunker's existence was already public knowledge are reports circa December 2002 about suspicious construction going on at the Veep's house.