British commanders viewed their American counterparts as "a group of Martians", enduring what now appears to have been a difficult working relationship in Iraq.
Tensions between the allied forces have been revealed in leaked documents taken from interviews with Army figures upon their return from peacekeeping operations.
The details have emerged on the eve of the first public hearings of the Iraq War Inquiry.
Some of the strongest criticism comes from the British chief of staff in Iraq, Colonel J.K. Tanner, who told the Ministry of Defence that "dialogue is alien" for some US officials.
"Despite our so-called 'special relationship', I reckon we were treated no differently to the Portuguese," he said.
The senior UK commander in the country, Major General Andrew Stewart, also gave a stark assessment, saying he spent a significant amount of his time "evading" and "refusing dumb orders" from his US superiors.
He added that Britain's ability to influence US policy in Iraq "seemed to be minimal".
The first public hearings of the Iraq War Inquiry begin on Tuesday
Maj Gen Stewart also said the absence of a secure communication line between his base in Basra and the US commander General Rick Sanchez in Baghdad was "incredible".
The frank comments come from Army figures involved in Operations Telic 2 and 3 during the first year of "peacekeeping" operations in Iraq, from May 2003 to May 2004.
Transcripts of the discussions, along with "post operational reports" by British commanders, were obtained by the Daily Telegraph.
Meanwhile, the head of the Iraq War Inquiry, Sir John Chilcot, has promised he will not shrink from criticising individuals or organisations if justified when filing his final report.
The first public hearings of the inquiry are due to begin on Tuesday.
Senior military and diplomatic figures will appear in the run-up to Christmas, and former Prime Minister Tony Blair is expected to give evidence in the new year.
Iraq Leaks Reveal US-British Splits: Ministry Of Defence Interviews Exposed On Eve Of War Inquiry | UK News | Sky News