South Africa authorities are investigating how nine soldiers were killed and 15 injured during a training exercise when an anti-aircraft gun went haywire.

An artillery officer who reportedly risked her life was unable to curtail the fatal firing spree involving a 35mm Oerlikon cannon at the army's Lohatla training base in Northern Cape province last Friday (10 October), Wired reports. The weapon discharged a burst of shells lasting one-eighth of a second before it ran out of ammo and fell silent.

The reason why the gun malfunctioned has become the focus of a South African army inquiry, and a separate police investigation.

Earlier theories suggest either a software glitch or small explosion might have caused the gun to malfunction, causing it to begin "wildly swinging" as it sprayed 15-20 high-explosive 0.5kg 35mm cannon shells. The incident followed running repairs on the gun, a part of normal procedures when the weapon jams.

In normal use the gun is designed to automatically target aircraft, helicopters, and cruise missiles and fire when they come into range. The weapon is capable of operating, and even reloading, without human intervention. Defence Minister Mosiuoa Lekota told the National Assembly on Tuesday that all the guns were set on "manual" at the time of the exercise.

The weapons were sighted on a target some 2km away and clamped into position "so that the barrel should not move from side to side," he explained.

The loss of life has prompted calls for a wider review of weapons maintenance and safety. "By nature of their job soldiers can be exposed to these incidents, but now a reality check is needed," National Defense Union General Secretary Pikkie Greeff told the South African Press Association, AP reports. ®

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