An undetected mechanical failure - which the manufactures of an anti-aircraft gun allegedly kept secret - led to the deaths of nine South African soldiers, according to Defence Minister Mosiuoa Lekota.

The nine soldiers, who were stationed with 10 Anti-Aircraft Regiment in Kimberly, were killed in October while taking part in Exercise Seboka at the SANDF's combat training centre in Lohatla in the Northern Cape. Fifteen other soldiers were injured.

The troops were manning and firing a Swiss/German Oerlikon 35mm MK5 anti-aircraft twin-barrelled gun when it went awry.

Speaking at a press briefing in Pretoria yesterday, Lekota said it was the second such incident to occur with the same type of gun.

He would not say where the other accident had happened.

The SANDF has 48 such guns, manufactured by Oerlikon Contraves AG (OCAG) in Switzerland.

According to the Department of Defence's board of inquiry, the gun malfunctioned because a spring pin, which is the size of a matchstick, sheared.

This caused the interface between the hand/motor actuator selector lever and the traverse gearbox to break during engagement.

This led to the disengagement of the control mechanism, rendering the gun uncontrollable during firing.

The spring pin is a connector pin in a selection mechanism that switches between manual and electronic control.

The board also revealed that the spring pins in 10 of the SANDF's 48 MK5 guns were also sheared.

Lekota said the manufacturers, which he declined to identify at the press conference, failed to notify the South African government that a pin failure had occurred on a MK5 anti-aircraft gun in another country.

They did not communicate maintenance tasks to prevent the pin failure from occurring or to correct the failure once it had occurred, and did not inform the government about any hardware changes to safety or user drills in South Africa, he said.

Lekota said the guns had been decommissioned now and were undergoing technical inspections to confirm the full scope of the defects.

He said the board recommended that the weapon system be redesigned to ensure safer handling and be subjected to an operational test. It also recommended that an updated product management intervention be conducted.

He said the Department of Defence was talking with its legal advisers on what action could be taken against the manufacturers.

Asked whether the relationship between OCAG and the SANDF would be terminated given the "failure in communication", Lekota said if there was a "reasonable explanation and we are satisfied by the manner of the resolution of the matter, then we will continue to do business, especially if the equipment is the best on the market".

Lekota said the SANDF serviced and maintained its equipment regularly.

Helmod-Romer Heitman, Jane's Defence Weekly analyst, questioned Lekota's announcement, saying: "It would be unusual for such a reputable defence company not to send out warnings.

"It is more than possible that warnings were sent, but were 'lost' in an administrative shuffle.

"This would not be the first time that this has happened in the defence force," he said, citing examples of technical updates being filed, but not implemented.

He said while the report may answer the questions of what went wrong, the summary did not and left more questions than answers.

"I am bothered by the fact that it didn't say why the gun traversed so far, killing so many people. In training purposes, large steel pins called dead stops prevent the guns from traversing beyond a certain arc.

"The question that now arises is whether the dead stops were in place. And if not, why not? And if they were, why didn't they stop the gun from traversing so far?

"This report's summary gives a reason for the failure, but it doesn't say why it led to the disaster," he said.

Retired Brigadier-General John Delmonte, a former SANDF air defence specialist, also wondered why the manufacturer would fail to communicate any defects.

"It is unusual and alarming if it is the case and even more so if the warnings were filed because of an administrative glitch," he said.

"There may be other issues of safety that need to be questioned".

OCAG spokesperson Irene Stockli said the company would comment on the allegations on Monday.