Friendly fire incidents are a feature of modern warfare

The two soldiers were riding in a Challenger II tank when it came under fire from another British tank, which either missed its target or ricocheted into their path.

Despite the regret on the part of the military commanders and the launch of an investigation, the deaths are viewed as "one of the realities of war".

The fast pace of modern battles has increased the risk of friendly fire incidents in recent conflicts.

Efforts to avoid

Yet this is still the first incident in which British forces have fired in error in recent years.

Known as "blue on blue" incidents - because in war games "blues" are the friendly force and "reds" the enemy - such deaths have become a feature of warfare.

In the 1991 Gulf War, nine British soldiers were killed by United States allies - matching the number killed by enemy fire.

Friendly fire incidents accounted for between 25% and 30% of American casualties during the same conflict, according to Jane's Defence Weekly news editor Ian Kemp.

In a fast-moving battle it can be quite awkward, particularly at night and in poor visibility, to distinguish one from the other

Ian Kemp, Jane's Defence Weekly

In the latest incident the turret of the Challenger is believed to have been blown off in the misdirected attack, which happened in pitch darkness.

There are some suggestions that depleted uranium shells were used - which would account for the complete destruction of the tank's turret.

Although the tanks operating in Iraq are fitted with identification systems, a technology failure is not seen as the cause.

Mr Kemp said many British and American vehicles were fitted with Global Positioning Satellite (GPS) systems making it easier to plot their positions.

These were introduced as a result of the "friendly fire" casualties in the Gulf War.

Most major combat vehicles have these, compared with around one in 20 in the 1991 Gulf War, he said.

A Ministry of Defence spokeswoman said on Wednesday: "We have acquired combat identification capability and we have been working very closely with America to make sure we do have effective arrangements in place."

Depleted uranium is thought to have caused the tank blast

Click for more on the effects of depleted uranium

The MoD also confirmed the three white panels seen on the sides of British vehicles were a new recognition device.

Defence Secretary Geoff Hoon has already said British troops will be given all the protection they can in a conflict.

Officials have repeatedly stressed that improvements in communications and logistics have greatly reduced the risk of friendly fire casualties.

'Still a danger'

But Mr Kemp said the likelihood of "friendly fire" incidents was still a "particular danger of modern operations" with a fast battle.

"In a fast-moving battle it can be quite awkward, particularly at night and in poor visibility, to distinguish one from the other," he said.

Speaking after Tuesday's deaths, Lieutenant Colonel Michael Riddell-Webster, commander of the Black Watch battle group, said the "friendly fire" deaths were a tragedy.

He said the commander of the Challenger tank troop involved was "clearly distraught".

Lt Col Riddell-Webster said: "The rules of engagement, even in war, are very strict. We have trained hard to avoid this kind of thing.

'Confusion'

"It is never done on purpose. No-one is blaming the tank crew."

He said "in the darkness and confusion, a mistake was made".

No one is blaming the tank crew

Lt-Col Michael Riddell Webster

Black Watch battle group

Click here for more about Challenger 11 tanks

Aircraft have always had Identification Friend or Foe (IFF) devices to send variable coded messages between aircraft and missiles communicating whether they are friend or foe.

Mr Kemp said: "Aircraft have always been fitted with these things and now they are trying to install a similar system on ground vehicles.

"The US is leading the way in this research and we, no doubt, will follow."