An internal British army document examining 37 years of deployment in Northern Ireland contains the claim by one expert that it failed to defeat the IRA.
The admission is contained in a discussion document released by the Ministry of Defence after a request under the Freedom of Information Act.
The 100 page document analyses in detail the army's role over 37 years.
It focuses on specific operations and gives an overview of its performance.
The six-month study, covering the period 1968-2005, was prepared under the direction of the then chief of general staff, General Sir Mike Jackson.
The document, obtained by the Pat Finucane Centre, points to a number of mistakes, including internment and highlights what lessons have been learnt.
It describes the IRA as "a professional, dedicated, highly skilled and resilient force", while loyalist paramilitaries and other republican groups are described as "little more than a collection of gangsters".
It concedes for the first time that it did not win the battle against the IRA - but claims to have "shown the IRA that it could not achieve its ends through violence".
In a statement, the Pat Finucane Centre - a human rights group - said the document "betrays a profoundly colonial mindset towards the conflict here and those involved in it".
"Loyalist violence and the links between loyalist paramilitaries and the state has been airbrushed out of this military history," it said.
In a statement issued on Friday, an Army spokesman said: "This publication considers the high level general issues that might be applicable to any future counter-terrorist campaign that the British Armed Forces might have to undertake.
"It is critically important to consider what was learned by those who served in Northern Ireland."