Conversation so far:
When did John O.
Brennan's time as a counterterrorism advisor to Obama begin?
President Obama then appointed him to be his Deputy National Security Advisor for Homeland Security and Counterterrorism, the President's.
What led to his appointment?
In August 2009, Brennan criticized some Bush-administration anti-terror policies.
Did he have a hand in any historically significant counterterrorism?
Brennan was present in the Situation Room in May 2011 when the United States conducted the military operation.

Question: What military operation was that?
Self-contained rewrite: What military operation was concerned in the Situation Room in May 2011?