WASHINGTON — About three hours after the US diplomatic mission in Benghazi, Libya, came under attack, the Pentagon issued an urgent call for an array of quick-reaction forces, including an elite Special Forces team that was on a training mission in Croatia.

The team dropped what it was doing and prepared to move to the Sigonella naval air station in Sicily, a short flight from Benghazi and other hot spots in the region. By the time the unit arrived at the base, however, the surviving Americans at the Benghazi mission had been evacuated to Tripoli, and Ambassador J. Christopher Stevens and three other Americans were dead.