The UK's famed Desert Rats armoured brigade will hold the southern city of Basra in any attack on Iraq, Ministry of Defence sources have told the BBC.
The unit has seen frequent action around the world
Also known as 7 Armoured Brigade, and armed with a mixture of Warrior armoured vehicles, Challenger tanks and artillery, it is the largest and most powerful of the British land formations being sent to the Gulf.
But the brigade lacks up-to-date communications and night vision equipment, making it more difficult to work closely with the better-equipped Americans.
MoD sources have told the BBC that it is provisionally expected that the brigade will get the job of holding Basra, the first major city inside Iraq, while the Americans bypass it on route for Baghdad.
Basra will almost certainly be the first city to fall, but will not be the most important action in any war.
The MoD stressed that other British units would also be involved in frontline fighting and says that all the plans are still very fluid.
Ian Kemp, news editor of Jane's Defence Weekly, played down any notion the MoD would reveal concrete plans at this stage.
He told BBC News Online: "The MoD will be giving out as much disinformation at this point as Saddam has done over his weapons programme.
He said any notion of "holding" cities during the conflict was also misleading.
"I don't see this as a war of 'holding', more a war of taking and taking rapidly."
But Mr Kemp said any inferiority in equipment would not stop UK forces working alongside US troops.
"It would be fair to say that everybody in the world is behind the US, but most countries in Europe are behind the UK.
"The UK certainly has certain equipment deficiencies."
Mr Kemp said the major problem was the delay in replacing the Clansman communications system with the secure Bowman system.
"There is not the over-arching secure communications system the Army wished to have in place. But it is not going to severely impact on the UK brigade."