A man with a gun caused the Tucson Davis-Monthan Air Force Base to be put on lockdown for several hours Friday afternoon. A spokesman said no one had been injured and no hostages had been taken as the civilian had barricaded himself in a room on the second floor of a building known as the “Old Dorm." The lockdown ended around 5 p.m., but officials offered few details. Gabrielle Giffords’s district director Ron Barber, who had been on base for a POW/MIA commemoration ceremony, said he left the base when the lockdown started around 10 a.m. The neighboring Pima Air & Space Museum stayed open during the lockdown, but public tours had been canceled and two nearby schools, Borman Elementary School and Sonoran Science Academy, had been shutdown. Security directed traffic off the grounds of the base.