TUCSON, Ariz. – Early on, it looked ominous when an Air Force base on the southern edge of Tucson was locked down Friday morning amid unconfirmed reports of gunfire. In the end, no shots were fired, and no weapon or gunman was found.

Traffic into the Davis-Monthan Air Force Base was limited as the unspecified security situation was first announced. Schools on the base were locked down. Ambulances and fire engines were rushed to the base, and a TV station reported that emergency workers were responding to a possible patient with multiple gunshot wounds.

This southern Arizona city was already rattled by January’s shooting rampage that killed six people and wounded Rep. Gabrielle Giffords and 12 others. And then there was the specter of the 2009 shooting in Texas at Fort Hood.

But, as it turned out, no shots were actually fired. And an ambulance that went to the base where 6,100 airmen and 1,700 civilians work turned out to be responding to a more conventional call: A woman had gone into labor.

Col. John Cherrey, base commander, said officials were satisfied it was safe after a “floor-by-floor, room-by-room” search of the building where a gunman was reported.

“No gunman or weapon was found,” Cherrey said. The commander, who held a two-minute news conference to discuss the five-hour lockdown, didn’t answer questions from reporters.