Defence Secretary Geoff Hoon has outlined details of wide-ranging structural changes to the British Army.
The Black Watch is to become part of a 'super-regiment'
He told the Commons reductions in heavy armour, heavy artillery and the infantry will be accompanied by an increase in specialists.
The number of infantry battalions will fall from 40 to 36, including a new "super-regiment" for Scotland, which will include the Black Watch.
Shadow Foreign Secretary Michael Ancram said it was a "dark day" for the Army.
Voicing Tory criticisms, he said the changes were driven by a desire to cut costs and were "dangerous" as they would leave the Army overstretched.
Britain's senior Army officer, General Sir Mike Jackson, said: "The Army has never stood still. It has always evolved to meet new challenges and it must do so again."
Royal Scots and King's Own Scottish Borderers to merge and combine with four other battalions to form Royal Regiment of Scotland
19th Mechanised Brigade to convert to a light brigade
4th Armoured Brigade to convert to a Mechanised Brigade in 2006
King's, King's Own Royal Border and Queen's Lancashire Regiments form two battalions in new King's Lancashire and Border Regiment
One battalion to go from Prince of Wales's Division
Mr Hoon's statement comes after Army chiefs met last Monday to discuss the restructure.
To Tory jeers, he told the Commons: "These plans will make the Army more robust and resilient, able to deploy, support and sustain the enduring expeditionary operations that are essential for a more complex and uncertain world.
"The move to larger, multi-battalion regiments that these changes bring about is the only sustainable way in which to structure the infantry for the long term."
The defence secretary said he understood the importance of regimental traditions but the changes needed to be seen in the wider context of "re-balancing the Army".
But Mr Ancram condemned the "dismal statement".
He said: "It is a dark day for our armed forces. It is also a day of shame for this discredited and ineffective defence secretary.
"Our armed forces deserve better than to be betrayed in this appalling manner by their government."
Liberal Democrat defence spokesman Paul Keetch warned that the cuts might leave Britain with its smallest army since the Afghan War of 1839.
"We must adapt for the new threats, but the old threats will not go away.
"Soldiers and battalions can be axed in a single sentence in the House of
Commons, but it could take years to bring them back," he added.
SNP MP Annabelle Ewing was ordered out of the Commons chamber by the Speaker after calling Mr Hoon a "backstabbing coward".
Sir Mike, the Army's Chief of General Staff, said: "We have inevitably had to make some tough choices to keep within the resources allocated.
"The underpinning rationale is based on an operational need for a more agile and flexible force."
The final decision on the restructuring was made by Mr Hoon and the prime minister after a recommendation by senior defence figures.
CHANGING SHAPE OF BRITISH INFANTRY
1 Two regiments merging and combining with other four to form one regiment of five battalions
2-3 Six battalions merging into two- and three-battalion regiments
4-7 Seven single-battalion regiments merging to form one two- and one three-battalion regiment. Remaining two battalions split to join other divisions
8 One battalion moving to form part of a new special-forces unit
9 TA being restructured to lose one battalion but no manpower