The problem of identification on the battlefield is a long-standing, complex one which has no single, easy solution, says the Ministry of Defence.
Training can help to reduce cases of 'friendly fire'
Since 1990, there have been 12 British service personnel killed in "friendly fire" involving US military in Iraq, and possibly a further three in Afghanistan, says Paul Wood, BBC defence correspondent.
So, in modern conflict, how do troops spot another "friendly" through the "fog of war"?
Sophisticated technology, organisation, better training for servicemen and women and the human brain all have a vital role to play.
Several communications and weapons targeting technologies help build up a picture for the pilot, captain or driver who then draws on his training and experience to decide whether to press the trigger.
An MoD spokesman said: "The man in his car has satnav to tell him where he is, but there isn't a satnav for the military and there couldn't be. There's just too much data.
"The way it works is that if you are on a battlefield you shouldn't be a target unless you can be positively identified as a baddie.
"If it was the other way round and you had to mark yourself out as friendly, you could become a target if there was a technical problem with your system. The military would never want that."
The simplest markers of a friendly vehicle - be it land, air or sea - are big orange panels emblazoned on the body.
"They're very visible and if you've got an orange panel everyone knows you're a friendly," the spokesman said.
However, that was not the case for Lance Corporal Matty Hull who died in 2003 when an American aircraft fired on his vehicle.
L/CoH Matty Hull was killed by friendly fire near Basra, Iraq
A cockpit video revealed the pilot had seen his orange panels, but was told by commanders on the ground that there were no friendlies in the area.
Charles Heyman, editor of Armed Forces of the United Kingdom, said no country had yet developed a fool-proof system to identify friendlies.
"Technologically, it's a terribly difficult business, because if you have any sort of electronic device which says, 'I'm here, I'm friendly, don't shoot', it's also going to be picked up by the enemy who can pinpoint your location and target you."
Since 2002, the MoD says advances have been made.
Firstly, a new radio system - BOWMAN - has been introduced, which according to the MoD, "removes any doubts regarding the location of our own forces".
It is said to allow troops to communicate more effectively with each other and with commanders to improve their "situational awareness".
Secondly, Successor Identification Friend or Foe (SIFF) equipment is being rolled out to aircraft and marine vehicles.
UK VICTIMS OF US FRIENDLY FIRE
2003: Airmen Flight Lt Kevin Main and Flight Lt Dave Williams killed when a US Patriot missile shot down an RAF Tornado in Iraq
2003: Lance Corporal of Horse Matty Hull killed when a US aircraft fired on two armoured vehicles near Basra
1991: Fusiliers Paul Atkinson, Conrad Cole, Richard Gillespie, Kevin Leech, Lee Thompson and Stephen Satchell, and Privates Neil Donald, Martin Ferguson and John Lang killed in an attack on a British armoured patrol by a US A10 "tank-buster" in the first Gulf War
Described as "an electronic question and answer system", it sends a radar signal to any unidentified target to which a friendly will respond automatically with a coded reply.
SIFF equipment is being fitted to more than 1,000 ships, submarines, aircraft, helicopters and missile systems, at a cost of about £500m.
The downside is that it is not suitable for identifying ground vehicles.
The MoD said: "There's just too much data from the ground - too many men, tanks, armoured cars - to process in any meaningful way. It would be impossible to get a real-time picture."
So-called "blue force trackers" are also installed in vehicles and aircraft to emit a beacon that can be detected by other friendly troops.
And individual soldiers are identifiable via infra-red tabs which can be picked out by thermal imaging and night vision cameras before an area is bombed.
The MoD has commissioned new technology, known as the Battlefield Target Identification System, which is designed to reduce so-called "blue-on-blue" incidents.
But, according to a Commons public accounts committee report published in May, this is still several years from completion and had been set back by failures to reach agreement on specifications with allied forces.
In May, the MoD suggested setting up a network of combat simulators to train US and UK troops involved in joint operations.
American forces have introduced a system called Cooperative Engagement Capability (CEC) which allows them to make better use of their existing sensors and communication devices to avoid friendly fire incidents.
A UKCEC project is currently in the assessment phase and the MoD is considering whether it should be commissioned to put British and American troops on a technical par.
Meanwhile, in the US, Pentagon engineers have developed a second system which uses a cockpit video transmitter to allow air controllers on the ground to see exactly what the pilot sees from the air.
Vehicles bear an orange panel to mark them out as 'friendly'
This Remotely Operated Video Enhanced Receiver (Rover) allows the controller to flag up both designated targets and innocent bystanders to the pilot before he fires.
Despite technological progress, the MoD says the military will always regard the human brain - and its training - as the most important factor.
So vital is the human element that something as simple as a laminated "combat identification card" is considered key to remind them of what they have learned about friendly fire.
Mr Heyman said: "It's probably wrong to go for a technological solution at all.
"Although it's impossible to eliminate friendly fire deaths, if people are properly trained, they can be greatly reduced."