More than 5,000 soldiers will be made redundant in the latest round of job cuts, the Government has announced.
The Army will bear the heaviest burden in this third wave of redundancies because the Navy and RAF have already completed most of their necessary cuts.
Up to 5,300 soldiers will lose their jobs, although anyone serving in Afghanistan when redundancy notices are issued on June 18 will be exempt.
It will also not affect soldiers recovering from a recent tour of duty or those preparing to deploy within the next six months.
No-one will actually be made redundant immediately and the announcement marks the start of the process for the latest round of cuts. Final decisions will be made by June.
Defence Secretary Philip Hammond said: "The Army is actively managing recruitment to reach the target numbers, but unfortunately redundancies are unavoidable due to the size of the defence deficit that this Government inherited and the consequent scale of downsizing required in the Army.
"We will have smaller Armed Forces but they will in future be properly equipped and well funded, unlike before. These redundancies will not affect current operations in Afghanistan, where our Armed Forces continue to fight so bravely on this country's behalf."
Chief of the General Staff General Sir Peter Wall added: "The Army is unfortunately reducing to 82,000 by 2015 and this tranche of redundancy is essential to achieving that.
"I fully recognise the unwelcome uncertainty and pressure for those who will be liable in the employment fields announced today. For some it may present an opportunity; for others it will curtail their Service prematurely.
"Our aim now is to apply the process as fairly as possible and to prepare to support those individuals who are selected as they and their families transition to civilian life."
In the last stage of cuts, in June 2012, 72% of the redundancies ended up being voluntary. Military leaders and politicians are hoping for a similar outcome this time round.
Anyone accepted for voluntary redundancy will be expected to work a six-month notice period and those selected for compulsory redundancy will have a full year to find alternative employment before leaving the service.
They will also be given resettlement support.
By the end of the process, the Army will have shrunk to 82,000 soldiers - a reduction of around 20,000 - mostly through a redundancy process but also achieved through slower recruitment.
The Ministry of Defence confirmed on Tuesday that further cuts to the Army, Navy and RAF are "likely" but gave no indication of timing.
The job losses are part of a strategic review driven by budget cuts which aims to produce a new look military by 2020.
The biggest commitment by some way is in Afghanistan - 9,000 personnel are deployed in the country - but the withdrawal process is due to start this year and by the end of 2014 most soldiers will have returned home.
Final numbers have not been announced.
In October last year the Defence Secretary announced plans to rename the Territorial Army the "Reservists" and double its members to 30,000.
There is also a hope that some of those leaving the military because of the redundancy scheme might sign up to the TA so that their experience is not lost.
By the end of the redundancy process, the number of serving personnel in all three services will be reduced to 150,000 from 180,000.
It will result in the smallest army since the 18th century and plenty of concerns over effectiveness.
It is not just serving military personnel taking the hit - the Ministry of Defence is in the process of cutting around 25% of its staff.
The aim is to save £3.8m a year and to make the department less top-heavy with management.
The UK still faces real or potential threats around the globe, demonstrated in the past few weeks by the hostage situation in Algeria and conflict in Mali.
Some, particularly retired service chiefs, question the UK's ability to face these threats with a reduced military and gaps in the equipment locker.
The Government will again need to convince detractors, home and abroad, that the UK military can still earn international respect despite its reduced size.
More From Sky News