Defence Secretary Philip Hammond has confirmed that army numbers will be cut by 20,000 over the next few years.
Mr Hammond confirmed that some historic Army units would be scrapped and others merged in the coming years as it scaled back its regular strength from 102,000 to 82,000.
He said the changes would mean an increased reliance on private military contractors and on part-time reservists as a result of plans set out in the Government's Strategic Defence and Security Review.
In future, the reserves would take on some tasks currently carried out by regular troops.
Mr Hammond also indicated that when it came to deciding which units were to be axed, the Army would take account of demographic changes.
He said: "While we are determined to maintain an effective regimental system, it must be based on the realities of today, and the primacy of capability."
Some tasks carried out by reserves would be handled by reserve troops.
Defence Secretary Philip Hammond explains why he believes the cuts are necessary.