Roulement is a term used by the British Army

British Army

The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

 to signify major combat units (usually battalion

Battalion

A battalion is a military unit of around 300–1,200 soldiers usually consisting of between two and seven companies and typically commanded by either a Lieutenant Colonel or a Colonel...

 strength) that are deployed on short tours of duty

Tour of duty

In the Navy, a tour of duty is a period of time spent performing operational duties at sea, including combat, performing patrol or fleet duties, or assigned to service in a foreign country....

, normally for 6-months duration.

The British Army has historically deployed infantry

Infantry

Infantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...

 battalions for 6-month and 24 month - roulement tours of Northern Ireland

Northern Ireland

Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

. Other Corps such as Royal Armoured Corps (R.A.C) etc when being used as Infantry are only deployed on 4-month tours. During Operation Banner

Operation Banner

Operation Banner was the operational name for the British Armed Forces' operation in Northern Ireland from August 1969 to July 2007. It was initially deployed at the request of the Unionist government of Northern Ireland to support the Royal Ulster Constabulary . After the 1998 Belfast Agreement,...

, this was more to do with the cost of re-training back to role than any operational reason. An R.A.C. Crewman cost an estimated £500,000 to train and skills were lost during any longer tour. Royal Marine commando

Commando

In English, the term commando means a specific kind of individual soldier or military unit. In contemporary usage, commando usually means elite light infantry and/or special operations forces units, specializing in amphibious landings, parachuting, rappelling and similar techniques, to conduct and...

 battalions and Royal Artillery serving as infantry in Northern Ireland are also roulement units.

The British Army currently deploys roulement units to Afghanistan

Afghanistan

Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

 as part of Operation Herrick

Operation Herrick

Operation Herrick is the codename under which all British operations in the war in Afghanistan have been conducted since 2002. It consists of the British contribution to the NATO-led International Security Assistance Force and support to the US-led Operation Enduring Freedom...

, Falkland Islands

Falkland Islands

The Falkland Islands are an archipelago in the South Atlantic Ocean, located about from the coast of mainland South America. The archipelago consists of East Falkland, West Falkland and 776 lesser islands. The capital, Stanley, is on East Falkland...

 and to Cyprus

Cyprus

Cyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...

 on Operation Tosca

British Forces Cyprus

British Forces Cyprus is the name given to the British Armed Forces stationed in the UK sovereign base areas of Dhekelia and Akrotiri on the island of Cyprus...

 with the United Nations

United Nations

The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

.