The defence secretary is to announce details later of how the Army will be restructured as it loses a fifth of its personnel over the next few years.
Philip Hammond will reveal the units to be scrapped or merged as the number of soldiers is cut from 102,000 to 82,000.
The Army 2020 review is also expected to result in the number of reservists doubling to 30,000.
Last month, the defence secretary said there was no way to "avoid difficult decisions as the Army gets smaller".
From a level of 102,000 troops in 2010, defence cuts will reduce the Army to 82,000 regular soldiers by 2020.
It will be about half the size of the Army of the Cold War era, which comprised more than 163,000 troops in 1978.
The defence secretary has said that the UK will still maintain an effective, well-equipped fighting force, but that it will be increasingly reliant on reservists, co-operation with allies and private contractors.
BBC defence correspondent Jonathan Beale said strategic thinking for Army 2020 had been led by "one of the Army's rising stars", Lt Gen Nick Carter.
"But, there's still no escaping that this review has been driven by cuts," said our correspondent.
'Split in two'
The government has said the regimental system will not be scrapped, and Prime Minister David Cameron has said no "cap badges" should go - in other words, entire regiments are not expected to be lost.
But units within regiments will be disbanded.
It is expected that the Army will lose five of its 36 infantry battalions, four armoured units will merge into two, while support units such as engineers and logistics could be cut by 30%.
The government's insistence on "regional balance" is expected to mean that while some full-strength English units with a strong recruiting record will go, others in Scotland that may have struggled will survive.
Army 2020 is expected to increase reliance on part-time soldiers in the future.
"The Army is being split into two," said our defence correspondent.
A "Reaction Force" made up entirely of highly-trained regulars will be ready to deploy at short notice.
The second element will be an "Adaptable Force" of both regulars and an increased number of Territorial Army reservists.
This force will provide troops for ceremonial duties, for standing commitment such as defending the Falklands, and include a "Security Assistance Force" able to send small teams to advise, train and keep the peace around the world.
'Ballooning up'
Professor Michael Clarke, director of the Royal United Services Institute think tank, said he suspected the Army would be a "one shot" force.
He said: "They could go somewhere, they can do something, at a very high level but they can't stay. Prolonged deployments will be difficult unless the government of the day is prepared to throw a lot more money at it and they can expand.
"They're trying to create an army that is capable of ballooning up again and coming back down."
Conservative MP Colonel Bob Stewart, a former Army officer who sits on the Defence Select Committee, said he was upset by the moves.
He said: "The right path forward is for us to have more armed forces than we've got but we're stuck, we have a real problem of trying to pay for them and equip them. That's the problem.
"I would much prefer us not to be making these cuts, and I particularly don't like the idea of cutting infantry battalions."
Lord Dannatt, former head of the Army between 2006 and 2009, said the Army would be able to do less but it would be agile.
"It will be capable of being involved in one significant operation at a time but it won't be capable of conducting two operations simultaneously of the size and scale of Iraq and Afghanistan that we have done over the last 10 years," he said.
He said a force of 82,000 regulars was "a very, very small" army
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