Around 300 soldiers had assembled at the Soldier Readiness Center on the base, where they were to have inoculations before being sent to Afghanistan, when Hasan, dressed in his military uniform, entered at 1.30pm and opened fire at close range with two privately-owned handguns.
None of the soldiers were armed and some barricaded themselves into rooms off the main hall of the building while Hasan repeatedly reloaded his weapons and fired indiscriminately for 10 minutes, killing 12 soldiers and a civilian.
Survivors described how Hasan had "a very calm and measured approach" as he fired scores of rounds. Lt Gen Bob Cone, the base commander, said one soldier had told him "I made the mistake of moving and I was shot again". Others "would scramble to the ground and help each other out", he added.
Officer Munley and a colleague were on the scene three minutes after the first shots were fired, but it took several more minutes before they could stop Hasan as he carried on firing.
Once the gunman had been brought down, soldiers rushed to treat their comrades by ripping up their uniforms into makeshift bandages.